The game is very CPU-bound, I get nearly the same performance at the lowest and highest settings. I've got a Ryzen 5 5600x and a RX 9070 XT, same performance degradation over time, and I've noticed the overlay shows it uses up to 14 gigs of VRAM and GPU utilization generally hovers between 70-89%. I tried switching to Vulkan as many games I've played in the past were generally more performant but in Deadlock at the moment this appears not to be the case. Average FPS seemingly isn't too different but the game has far worse 1% lows and feels quite jittery to play. As of now DX11 is the only playable option for me.
I'd really like to see some improvement in this area because while the 5600x isn't by any means a new CPU (atp it's nearly 6 years old), it's probably still better than most Steam users and I have friends with older PC's who can't keep the game at 60 FPS with lowest settings at 1080p 50% render scale.