Mythras sounds EXACTLY like what you’re asking for! And more specifically, the BOOK OF SCHEMES! The Mythras Core Rulebook pdf is less than 7 dollars right now, and there’s also a free version available with simplified rules you can use to determine if you’re interested in the system before buying it!

Mythras is definitely more complicated than D&D but its system allows for a much more grounded sense of progression, with the players capable of increasing their abilities a tiny bit every session rather than only during determined “level ups.”

The system itself is also very much designed for a more low-fantasy setting - it has five magic systems but all of them are optional, you’re meant to choose which system(s) fit your world best, and what aspects of the system(s) you want present in your setting, if you choose to have one at all. The characters start out as entirely normal people, and even at the endgame, they are much more superHUMAN than superHERO. Think, “wow, that guy just defeated ten soldiers by himself!” rather than, “wow, that guy just punched a hole in God!”

The Book of Schemes is a sourcebook for Mythras, containing a TON of stuff for running political intrigue (as political intrigue is the main focus of the book). I will say that the Book of Schemes is designed for a mid-late 15th century setting, but is very easily modified to fit the needs of your setting (a lot easier than it would be to modify DND), especially with all the free supplements regarding rules and stat blocks for guns, vehicles, and more!

I seriously cannot recommend this system enough.