Its not just that.
If they are going to retcon it, at least write some god damn lore to at least pretend its not just shoehorned in because of modern politics.
Primaris marines are a classic example. They want to sell more marines, so they at least write an entire backstory as to why. They don't try and pretend that LOL PRIMARIS MARINES HAVE ALWAYS EXISTED.
By just being lazy and saying "Lol bigot, there have always been female custodes" it doesn't feel like the progression of lore. It feels like its identity politics. If they do it right, no-one serious would care. Eldar, SoB, Dark Eldar, all model factions with females. No-one cares, because they don't feel like they are female for shoe horned reasons. Women in the reserve units of the IG in the novels make sense, because the reserve units are basically just calling up every man, woman and child that can hold a lasrifle.
Whats next? Tyranid Carnifex with tits? Because the hive mind was secretly female all along?