[XPS 15 9570] Underperforming for games, GPU usage immediately 99%-100%

Sorry if this is asked a lot, but I couldn't understand whether my problem is the same one that most of the other complaints are about, during my search online.

When I first got my XPS, games would run beautifully on high or even ultra settings with good framerates, but for a while, this has simply not been the case. Even on low settings, there is considerable lag with mediocre to straight up horrible framerates. I checked the usage percentage using task manager while the game (Sekiro in this instance, but it's a similar story with Assassin's Creed Origins) and the Nvidia GPU had a usage that was right at the top.

I then tried the MSI Kombuster test and on both 720p and 1080p settings, it would run only between 10-15fps during the test with the GPU usage being 99% or 100%. The CPU usage seemed fine and the integrated GPU wasn't being used. I tried changing the power manager settings to high performance, but it didn't change much. I tried using a couple of different profiles on ThrottleStop and also without ThrottleStop but no difference. Performance didn't seem to change regardless of whether GPU temp was in the 50s, 60s or 70s.

Of course, I know this isn't a gaming machine, but come on. It should be able to handle the odd game here and there on modest settings (though really it should be high settings). This is pretty upsetting, but I'm optimistic that it can get sorted out. Asked on reddit a couple of days ago, but unfortunately no replies. Thank you.