My take on this is that, besides Twitter's general product stasis, the reason they've been conflicted on this is that the experience for new users and power use

My take on this is that, besides Twitter's general product stasis, the reason they've been conflicted on this is that the experience for new users and power users is completely different. For a new user, any response is great and Twitter wants to encourage that. For a power user, they have more than enough responses ("randos in my mentions"). I do feel that greater control over "notifications" is the obvious approach here and glad they're introducing controls like 'mute conversation'. Medium has an interesting approach with comments where you can see all comments vs. author-approved comments. Twitter probably doesn't want to make their UI complex with a lot of options but more granular control on replies (maybe even an ability to disable replies and quote tweets) would probably be useful.