gaming on linux has gotten MUCH, MUCH better over the past handful of years. I’ve been on linux exclusively for 6 years and in that time ive gone from using Lutris for everything and only installing the few verified titles through fairly complex wineconfigs other people made, to a brief check of protondb before installing whatever i want from Steam and having it work out of the box. basically the only things that don’t work anymore are competitive anticheat softwares, like Valorant’s.
It’s not this significant (3x). it should be closer to 7%. My guess is that OP is using something like btrfs, whose data used is calculated differently due to the CoW nature, and btop++ is using using a generic tool to estimate disk usage rather than the btrfs utility that DUA is almost certainly using.