TLA+ is for when you have a 1MLOC database written in Java or a 100KLOC GC written in C++ and you want to make sure your design doesn't lead to lost data or to memory corruption/leak (or for some easier things, too). You certainly can't do that with Dafny, and while I guess you could do it in Lean (if you're masochistic and have months to spare), it wouldn't be in a way that's verifiably tied to the code.
There is no tool that actually formally ties spec to code in any affordable way and at real software scale, and I think the reason people say they want what doesn't exist is precisely because they want to avoid the thinking that they'll have to do eventually anyway.
[1]: Lean and TLA+ are sort-of similar, but Dafny is something else altogether.