Lore issues aside, the main reason I hate the Timeless Child is because it restricts creative writing opportunities.
Besides mortal danger no longer being as big of a threat to the Doctor, it means that there won't be another chance for the Doctor to confront the end of their life in a final incarnation and find a creative way around it.
Imagine the Doctor on their last life (again), after several series of buildup with unfinished adventures, loose plot threads, and threats that were not entirely beaten - either through accident or necessity - or were replaced by new ones. The Doctor regenerates into their final incarnation and realises they've got so much unfinished business. They rush to complete all they've left before their last breath, only for more things to come up against them. "It's not fair", they think, "that I should die when I could do so much more good in the universe". And they go a bit dark. They remember all the times their old frienemy tried to steal their regenerations after running out themselves. But had they? We've never seen half of the Master's incarnations in media despite him running through a regeneration cycle (perhaps 2 by this point), and the Doctor decides it's time to return the favour. They travel back and steal the Master's regenerations, giving themselves more lives (not a whole cycle, maybe just 5 or 6 more), robbing the Master of his and creating some of the conflict they've previously faced.
You never remove the problem, only postpone it, allowing other writers to come up with new ways to get round it. That's why I find the Timeless Child to be such a copout and boring solution to this problem. Because it restricts storytelling, not expands it.