Ok I managed to fix the issue. Apparently I had to set my CPU governor to “performance”. I installed the “auto-cpufreq” package with:
sudo pacman -S auto-cpufreq
Then I made it change the governor depending on usage by running
auto-cpufreq --live
And boom, the game is running even better than it was on Mint, no framedrops and a consistently high framerate. Couldn’t be happier.