I think lowering the repair times would be a tricky call. Having a long repair time for large units acts as a counterbalance against the natural advantage that big or giant realms have on the battlefield. If it takes them many days to do the repairs on an army of 100-200 troop units, it at least gives the smaller realms an opening to do something. I have a duke who's regularly fielding 165, 1000+ CS, infantry and has all the gold he could possibly need. Repair times are the only thing that slows him down. Imagine large or giant realms, with all their gold and recruitment centers, having everyone leading 80-200 troop units and having a fast turnaround time on the refit due to lowered repair times. Everyone playing in a small or medium realm may as well give up.
The underlying problem here is that the game is starting to become non-viable on most islands because there aren't enough players/characters. That's the only reason that everyone is trying to maintain massive units.