- a game like 40k is nearly impossible to balance anyways
True, perfect balance isn't possible. But it's also not needed. Honestly, all that's really needed is just to prevent degenerate gameplay from popping up. Prevent unit-spam, prevent stuff like ward-save spam, prevent weird daisy-chaining nonsense, prevent units/factions from breaking the core gameplay (e.g. "weird" armies like knights/SoB probably shouldn't exist). That sorta stuff.
However, it's honestly fine if a faction has a high winrate. If only because you can't balance around a faction being easier to play, or a faction being particularly popular, and how that will inevitably skew your "objective" balance statistics.
What's interesting is the difference in balancing appraoch between 40k (or AoS) and for example, bloodbowl.
In 40K they focus heavily on "objective" measures of balance, and religiously gather statistics. They also try to keep everyone at (roughly) the same level of power.
In bloodbowl they flat out state that some teams are terrible. If you play with them you handicap yourself. Instead they focus on making the teams fun and interesting to play with. You're probably not going to win a tournament with the weaker teams, but they provide an interesting and different challenge.
Weirdly enough, I don't think I've ever heared anyone complain about a bloodbowl release. Whereas every other major 40K/AoS release causes the internet to be flooded with posts about how the new faction is the FoTM who dominates the meta.
And that seems to hold more generally for games. Games that accept that not everything will be the same powerlevel, but focus first and foremost on everything being fun, tend to feel more fair & importantly more fun as they naturally avoid degenerate (and degenrate-like) gameplay. Whereas games that are explicitly designing around a "healthy" competitive meta seem to fairly consistently run into issues where degenerate (or degenerate-like) gameplay keeps sneaking its way into the game.