Flask (python) or even CodeIgniter (php) are my frameworks of choice for this sort of thing. They may be a bit old and organizing a large project could be difficult but nothing can beat them on performance!
Twitter too was on Rails in the initial days which helped it took off, and then realised they need to move to JVM(Scala) to scaled and they have been performing brilliantly since then.
Now, that MS has bought them, why don't they use the brilliant tech MS has (.NET, .NET Core) and be more reliable?