I don't field a 30 or 40 saurus unit because I don't have them
I saw saurus being run down in first combat many times. But usually against O&G who brings a lot of numbers.
But they are good against white lions because they are squishy. Against any other S5/S6 unit with a little more survavilty they just disappear. You said the example: Savage Orc Big'Uns.
I haven't lose any battle cuz of purple sun yet, but the threat is there. The friend i play against most of the times in our local group has WoC. He always field that pesky Nurgle DP. Which you know... it flies.
Its so hard to counter since he can just charge in the flank or the front, pin your unit there, and start grinding it down. As it is a lone model it doesn't care about 60% of the miscast table. heck, it maybe even help it more with those S10 templates. If not that turn, would be the next, or the next as he could engage in turn 2 if desired.
Purple sun would go through the engaged unit aiming another unit probably stuck with a chaos chariot.
Not only is near unkillable for us in combat, it could kill any of our units, and then there's Purple Sun.
Lizardmen has a rough time with that guy. Now throw skullcrushers, 2 chimera, chaos chariots.
Saurus don't have any chance.
Your bet is to bring more. Ok, They still don't have a chance and you have not taken other options who could help more than saurus just for 1 or 2 more rounds of agony.
They performed well in all games but one, against O&G they were run down in first round
The only game I lose was against WoC.
I would not claim the saurus to be an all comers solution, which they are not. Those are the Skinks.
My favourite army buildings is around Oldbloods. I can't live without them. The frog is for fancy games. I don't get on magic. We are more similar than this thread may say
I'm glad to know we have more in common than I thought at first

and congrats on all the wins it is good to hear when our cold blooded minions win, WoC are certainly the hardest army for me to play against with lizardmen.
If you get more saurus then try them out, against any other S5/S6 unit besides savage orcs they do very well, WoC they will grind down with and eventually lose but it will take a while and I usually can counter charge in after two rounds to help out. Run the numbers against hammererstars and saurus win, same with ogre units, the only good counter against saurus is to not let them hit your unit (which means characters in the front ranks, which increases the unit cost and means your opponent is taking most of his combat power to try and deal with your core allotment)
That Nurgle DP is rough, but as you mentioned Oldbloods are awesome and a good pair going after him once he commits to a combat usually brings him down 1st turn for me. Of course that means I need to field units that can take him for a turn or two, so saurus instead of a skink cloud lol, seems like we just like to play different styles.
And the last time I played WoC his Chimera died against my saurus along with his chariot, sure they hit hard and hurt a lot but I just remove those back ranks and hit back with enough force to kill him by round 2-3. Skullcrushers though, ouch they eat my saurus for snacks, I definitely agree with you on them, for me I use Krox, characters, Stegs to deal with them, but I run enough saurus to be able to throw a unit away to their charge and/or overrun so that I can countercharge.
See I like skinks but for me they are not an all comers list, too many of my opponents know exactly how to crush them, and do it fast, for me to rely on them to win a game, I need a unit that will still be around turn 5-6.
I think we play in vastly different metas which would explain our different view points. I'm a competitive gamer and most of my games are under ETC comp and against ETC players, even on the rare occasion its not tournament or practice both players tend to bring the strongest filth they can. Most list revolve around msu with one hammer unit. The only big infantry(20+) I see are empire bunkers, warriorstars, lionstars, hammererstars, skaven slaves, savage stars, gorstars, skelly buses, zombies and plaguebearer stars. I either dont care about the units(slaves/zombies) enough to bring 400+ points of saurus to handle them or the saurus lose.
As for the Saurus vs Dark riders with 2 characters it works like this. Both guys are on pegs so the front rank is Dreadlord,champ,BSB. they go in and kill some number of guys say 7 from your numbers, the saurus do max 1w back as they kill the champ. If they have 12 DRs(more is common enough) going in they break steadfast and run down your 40 man unit.
Death is still the best lore in the game hands down, no questions asked. 5 out of seven spells are legit game winners so purple sun will always be present. With Nurgle demons, VC, Ogres, CHD, Dwarfs and O&G all being common armies who die in droves to I tests people bring lots of them, not to mention star dragons, kholek and throgg who are very tough to kill unless you can I test them off.
As for catching Morathi with Saurus, I assume thats a joke or you're relying on a combat reform at the end of your opponents turn.
As for my solution to the gutstar, kill the support units, double flee the guts and shoot it and psun(anwser to warhammer!!!). Why fight something that is only good at fighting?
We certainly do play in different metas lol, if you brought kholek or a star dragon to one of my games there would be a whole lot of surprise and a gaping hole where they were fielded by turn 2. Throgg though, he is awesome, his model is killer and his rules are nuts, I love fielding this guy and even playing against him is fun, special characters should all be as effective as he is. But yeah we play hardcore rules and no comps, there is no room for "fair play" or a tournament settting is trying to make things balanced, we also half the time play full end times rules with full unbound that really gets ugly
So when is the last time you fielded 400+ points of saurus against those units? Because I face them a lot and all my opponents know that to win they need to take down my saurus before I get them into combat with their big deathstar, only exception is savage orcs and I don't ever let them keep their frenzy past turn 3 at which point saurus will win.
I've had that DE tactic used a couple times, most of the time they field a lot of smaller DR units instead of larger, but if they do go for larger then I deploy in a staggered pattern with overlapping sectors to counter charge. All it takes is a single saurus character, or skink character in a unit to crush that plan since they hit at a higher I and kill the champ, which is why no one tries that with me anymore, stay 1 step ahead of your opponents plan and always have a solid plan B yourself and these tactics are easy to beat. That DE unit either charges a saurus unit it can break and then it gets counter charged or it hits a saurus unit it can't break and gets crushed in 3 turns. I keep hearing the same old DE tactics on this forum, and it feels like we are just not adapting our own play styles to beat them, if the tactic feels like a gimmick it probably is and that is easy to overcome, be flexible in your play and mentally adapt, don't get caught in a rutt and always look for a unique solution.
I agree, death is awesome, it is not the best for everyone but I would say yes it is the best overall, and even still I have not had trouble dealing with I test spells, how many times in the last 3 tournaments have you been tabled by them?
No I have never caught Morathi with saurus, but I have caught her with other things after she tried and failed to get a spell off that would have walked down my battle line, it is all about set up, and a lot of the time luring my opponent into a trap by offering up something they think is too good to pass up or a mistake on my part.
that is an excellent solution to the gutstar, but between my way or yours if both result in a win I'm going to take the run up and hit them repeatedly in the face until their aggression stops answer lol
Sorry this post is so long, I love these discussions and feel everyone has so many good things to add that I like to address all of them. There is no wrong way to play warhammer but there are better ways to play certain units