I think before gen 7 they weren't really considering actually changing abilities.
Gen 7 is when they started seriously looking into competitive balance, most of the moveset, stat and ability changes have been done with competitive in mind rather than just "in game fun" perspective.
I think it's not so much a case of them "not being willing to retcon" but rather them only recently realizing that they need to do more than "just add new pokemon and gimmicks" to spice up competitive metagame to get it become a real e-sport.
Gen 9 has also been the first time they've shown they are willing to tamper with movesets as well. While yes, outside of smogon, transfer moves have never been allowed, outside of moves strictly not appearing as tutors/TMs at all in a given generation, they used to be more or less consistent with returning ones: if you could learn move X in the previous generation, and it returns as TM (or equivalent), you were still able to learn it the next generation. Gen 9 has shifted, where even moves that were in gen 8 (like Scald) or were actually introduced in gen 8 (like Grassy Glide) have seen a shift in distribution / power in order to spice up or alter the competitive scenario.
Considering this has mostly been received positively by the VGC players, I'd expect the trend to continue.
Yeah fair. I'm not a particularly competitive player so I'm more just thinking actual game mechanics. Pre-Gen 9 they basically just added abilities to Pokemon as a way of "filling in" species who only had one regular ability, but there were occasional balance changes like Scolipede getting Speed Boost or Gengar getting Cursed Body. I was purely thinking in terms of "what changes would make certain Pokemon more fun/interesting to use than they currently are" and "who could use a shakeup". But as you say, they're seemingly taking more notice of the competitive metagame now.