They're not necesarly weak and very much have their uses. Knights are probably our single best pick if you want battleline that actually does something, but don't want your battleline to be the focus of your army. Knights have good enough stats to be able to actually put up a fight at minimum size without requiring several supportive buffs which none of the other battleline options do. There's however 2 issues that Knights have. 1) They only have 1 effective tactic if you want to use them as the backbone of your army, namely stacking command abilities on them. Which is expensive & unreliable as there's too many things that can go wrong. 2) They're merely "decent". They don't have anything shiny like loads of rend or special attacks to make em stand out, and their charge attack is simply too unreliable to have that be their thing (even in a firelance). However, if you simply want capable battleline then they are definitly a good pick. Just don't threat them like you would a 40 man saurus warrior death star or an elite unit like gore-grunta's, dracothian riders or skull-crushers. In short, they're actually good battleline instead of a tax if you don't want your battleline to be the focus of your army. Temple guards are also actually rather good. They have amazing stats. There's just one problem. Mortal wounds are so stupidly common in AoS its just kinda stupid & a great deal of those attacks are ranged on top of that. Which just makes them rather difficult to use as you have to put in excessive amounts of effort to avoid the mortal wound spam... If however you can manage to do this then they are essentially immortal, which is what makes em so hilarious in skirmish.