Pretty good, atleast for me. Almost all vsts I’ve downloaded work really well, windows vsts included with yabridge, sometimes the ui is janky (could be 'cause i use a tiling wm and pop-up windows don’t agree with it) and a couple of random vsts don’t work at all (includes both linux and windows vsts so idk if it’s bad programming or a linux thing.) Reaper also has support for claps and lv2s which both work well.
If Deadlock is coded anything like Dota 2, it might be a problem with the game. Dota 2 has had the problem you’re describing for years on both Linux and Windows. Haven’t encountered Deadlock being as bad, but might still be the case. Or it’s something with proton.