What happened to Rust's performance & FPS in the last 2 years?

I played rust somewhere between 1.5 and 2 years ago, on low graphics settings (but not absolute rock bottom) in full screen and didn't have any FPS issues. I did have to use the old "grass.on false" command in console otherwise the grass killed my frames.

Today, I decided to try the game again to see what's new. I'm still using the same computer I was then. I've turned every graphics and performance settings in the options way down to the bare minimum, and I still only get like 10 FPS and it's not even consistent. If i go into windowed mode and make the screen a tiny little window, somewhere around 800x600, my frames will move up to 30-40.

I know the game is in 'alpha' but I would have thought after 2 years we wouldn't have back-tracked in performance and gotten to a point where it's not enjoyable to play. Seriously, playing in 10 FPS (with random lock-ups of no additional frames for like half a second) is just awful. And playing in a tiny 800x600 window isn't the most thrilling experience either.

I've never played any other game where performance is this low, especially while on the lowest possible graphics settings.

So is this something others are experiencing a lot with rust lately? And is there anything I can do to improve my frames?