Easy, Reaper has no Session/Launcher view like Bitwig and Live have. There’s a piss poor script that costs money to use, that gives less than half the functionality of Live or Bitwig. This is every DAWs downside but it’s exaggerated in Reaper, it “has” the ability to almost do it, but not nearly as fleshed out and with many many more steps. The same is true with articulation mapping, there’s a mediocre script for it that doesn’t come close to the ease of use and functionality of Cubase, Studio One or DPs articulations management. I would argue this is true of its Comping, and retrospective record as well.
There are plenty of areas where Reaper beats the snot out of everyone else, CPU management, audio rendering options, GUI customizability, I love the various containers for parts of a song on the timeline, the wet/dry mix built into every plug in window the ability to customize the interface etc etc. but like every daw there are areas where it’s behind the competition with, that’s life.