As for the absurd win rates, I really think GW needs to look at these and try to fix them the best they can. Obviously there will never be perfect balance in a game like this, but you can attempt to make the difference as small as possible.
I don't know if they can be called absurd yet, especially with so little data and entirely new rules to get used to. However take Krigsluntan GT with 8 players in the data attending that tournament. We see 1 with 5/5 wins who is already known to be an expert player. Then we see 0 with 4 wins and 5 with 3 wins, 1 with 2, and 1 with 1 win. This was one of the most played factions at that tournament, probably a lot of players excited to get out there with something new, including top players who also hardcore the hobby to already have an entire painted force.
The 62% win rate is then down to the large "midfield" of 3/5 game wins. Against a brand new army that is not absurd, if that was 5 players with 2/5 wins would that be absurdly underpowered then? Keep in mind we only saw 1 player achieve 5 wins, a player who has done so with other armies as well. 7 battletomes had win rates of 60% or above, with Tzeentch being at 70%, does that make them absurdly overpowered? Obviously this dataset is too small to make such a claim in favor of either agenda.
Also worth of note is the small amount of players from the top dog Slaanesh, with only 3 players but one of those not only getting 5 wins but also winning 1st place. Blades of Khorne also doing well, but with a larger distribution of players landing in all win rates.
If anything even for such a low amount of data I would just about dare to say the reapers are strong, above average, joining armies like DoK, Fyreslayers, FeC and Skaven for example. I doubt we will see them steamroll any of those and especially not Slaanesh. Bonereapers have no teleporting, no deepstriking, no fight first/fight last mechanic, no attack twice either in combat or in hero phase abilities, no summoning and relatively low mortal wound output outside few niche builds like Nagash (then the army is more Nagash than reapers anyway).
The thing keeping the reapers in that esteemed company is the Petrifex Legion, gaining the +1 save and universal access to +1 rend command, which I will agree is absolutely terrible internal balancing of the book and to a degree external balancing. I'd much rather see this evened out somehow, as the best defensive trait and best offensive command in 1 legion makes no sense.
I doubt we could see any other legions doing well, as 4+ saves across the board and low wound count will not hold up for long. Any Seraphon player should know that high saves on expensive 1 wound models does not go far, we do not spam saurus guard with 2+ saves, ignore rend 1 and 3 attacks with d3 damage for a reason. Meanwhile people advocate the reapers to end up in the saurus guard bin, which is obviously not a solution to anything.
The reapers are very average in anything but Petrifex and secondly in a Mortek Praetorian army with Katakros as the general (this setup seems the most balanced version of them in my opinion, with a "tax" for the save and no extra rend access). Increasing costs of base warscrolls will only serve to balance towards petrifex, instead an errata would be more suitable, to even out the legions usefulness.
We see a lot of complaints from Ogor players who obviously are playing with the new book as well, but putting Gutbusters and Gluttons with 0 rend vs petrifexs mortek guard is obviously an uphill battle in this matchup. This is why I think Petrifex should instead of +1 save to begin with get changed to reduce rend by 1, this makes it far more forgiving for low rend armies. At the same time their command ability should be something like what the Praetorians have now to double down on the playstyle and then give Praetorians something more interesting.
