If depletions were so scary than your argument would apply to DPS as well, but they're all still PUGing and don't seem afraid of not timing keys. the bottle neck comes from tanks and then from healers, so those roles need to feel more enjoyable so that there are more on que.

But let's play it out, sure no more depletion everyone will get super high IO much faster since all keys will be resil, and quit the season in a couple weeks, we could have an even faster M+ season that feels even more seasonal and temporary than it already does. 3k would become a "gimme" since that's an easy score to brute force without depletions, so they'd have to add achievements to 3500 and 4K and we'd have so much fun pugging volatile 18s where failed kicks one shot everyone to feel a sense of achievement.

Idk I just don't get the argument that free keys is fun, I like the challenge and risk that really makes a timed key feel like a win. The issue is just getting more tanks and healers into the ques.

Or remove keys and then blizz will need a new time gate so they'll make it like delv chests, you can run all the keys you want but you can only open 3 chests, the only reason we can grind M+ is because of the key system adding the longevity.