i play on max graphics, heavily modded and i experience little to no lag.
Sometimes when i join a server that doesnt have my mods, the game will get laggy over time but a simple relog fixes it.
Before i add mods, i never experienced a single lag spike other than during world save.

Also you cant compare a small dev team of 6-8 people to a dev team of 20+
ofc the game runs worst than gta.... its a indie and gta is a millions dollar company....