This comes down chiefly to two things:
- Moving items is slow and clunky
- Often, moving an item doesn't register properly - especially with "pop-out" slots like Welding Tools and Plasma Cutters
I'd say problem #2 is definitely a priority - I really don't want to accidentally put my welding tank into my inventory if I want to put it in my Welder, or worse yet, drop it on the ground because it didn't properly click, all the while trying to combat a severe breach.
Problem #1 is more complex but lower priority. I'd recommend making the inventory slots larger, for a start.
TL;DR - improve the speed at which items can be equipped/moved and fix weird things happening when moving items.