DPS checks are still a thing in WoW. LFR has them lower but you can still wipe to bosses because of poor DPS. Mythic for sure has strict DPS checks (at least prior to Blizzard nerfing it to the ground in order to fill Alliance Hall of Fame). The balance between the 21 talents you can currently pick is usually not that large but it could impact a dps check for a fight. You could likely over come it with gear/skill in most cases.
It is harder to balance a dps difference between good and bad talent choices because it means good choices would always have an advantage. So the bad choices would have to be ignored for dps checks in order to provide a challenge to the good choices. Is it acceptable to make it so talents matter more in Heroic/Mythic +8? So players that want to take the leap to those things no longer can play as they did? Will the community even pick those bad talents if it means good ones give them a big advantage in that lower content? I know the answer based on how the community has reacted over the years.