Monster Hunter: World is a great game, but its PC port is just OK. Steam modder Kaldaien, who you may know from the 'FAR' resolution fixes he released for Nier: Automata, is working to improve the port, and recently released a mod pack containing a medley of fixes and features.
Initially, the 'Special K' mod pack focused on fixing World's habit of crashing when you alt-tab out of the game, as well as enabling HUDless screenshots and custom shading (which, Kaldaien advises, you will need to tweak because the default options look, uh, off). It has also been updated to improve CPU usage via controlled threading.
"The mod now, by default, limits job threads to the number of logical cores on your system," Kaldaien said. "It can be configured to use physical cores or you can turn the feature off completely."
Kaldaien says he's "working on various improvements" for World, with aspect ratio corrections on the list of "possible future features," so the mod pack may well be updated more in the future. You can find download and installation instructions in this Steam post.