Yes, the main problem I've seen with focusing too much on length (of functions, files, or whatever else) is that people start spending tons of time rearranging

Yes, the main problem I've seen with focusing too much on length (of functions, files, or whatever else) is that people start spending tons of time rearranging the big messy drawer into n smaller messy drawers while totally avoiding the difficult work that needs to be done to actually organize the drawer(s). All other things being equal, smaller functions and smaller files are a little bit better, but what really matters is architectural and conceptual complexity. Keeping those in check is all about using the right data structures (and doing painful refactors when you realize you've got the wrong ones). It has almost nothing to do with how files and functions are organized.