I've been playing Civ 5 on the Mesa radeon driver since it came out on Linux with great framerates. That being said, My FPS at 1080/high has gone from ~45 to over 90 in the last two years on the same 290 card.
I can replicate this experience. Enemy Territiry with radron would give you maximum 30fps in 2014 or so, forget playing with rain or on a populated server. Now I get 90fps at 1080p comfortably.
Heck, I've been playing Mankind Divided on a 580 using open source drivers. Rocket league should be fine even with the smaller integrated GPU.
Civ 5 is buttery smooth on my 2015 Radeon R9 Nano at 4K resolution, with the amdgpu driver and Mesa/X11 on Arch Linux.