Playing at a higher resolution depending on if the game that you are playing is CPU and/or GPU intensive drastically tanks your FPS because more processing power is needed, playing at 1080p is usually the best but like you I also have a 1440p monitor and it's lovely.
What FPS was you averaging when playing on the lowest settings just out of curiosity? I tested this last week and of course my/our game would look like shit running down a wall but I had a stable 100 FPS even at 3440x1440, I didn't have time to test it with x amount of AI/Bots in raid which I might do at some point.
Yeah I wouldn't recommend turning the amount of bots to Horde or High there's no point to it, always leave it to Like Online. I believe Tarkov is more GPU intensive than CPU so that's more than likely why you are seeing 20-25% usage.
I actually just tried the game with bots number on "medium" and "as in online" and it's almost still the same FPS lol, maybe marginally improved by 5 FPS? Anyway it's hardly noticeable and I honestly would be surprised if it improved since it seems to me the game's FPS is basically locked down by something considering graphics settings don't affect it at all. So doubt CPU related stuffs would help especially since CPU usage is really low, at 20-26% (which is tied to the amounts of bots, whereas GPU controls graphics-side of things.
I get between 30-50 FPS with everything on low and running 1080p, depends on the map too. Basically the same as everything on ultra/high lol.