No making it harder is only going to make the hordes bigger.
I like the idea of localized ENY helping to control numbers in small areas instead of map wide. While being "hindered" would be a PIA, it would certainly get the horde down.
I also think tying the base/field to enemy numbers a good idea. If you bring in a horde to capture a base the hardness goes up, percentage needed down in town goes up. Bring a smaller force and you need less of the town down, and hardness returns to normal for hangers. It would bring the mission more in line to where defender might be able to defend a bit. It would also give smaller squads/group a chance to take bases.
I'm not sure that harder targets would cause larger hoards. I think there is a point where the hoard masters can no longer draw more people into their base taking missions. Each side still has a percentage of pilots who will not join a hoard. I can't remember the last giant mission I joined. In fact, the only base take that I have been a part of this tour was a small squad only affair (8 pilots I think) to sink a CV and take a port all in one fell swoop. I flew the goon. First time I had done that in a very long time.
But I am willing to agree that it might cause bigger hoards. But like I said before, for me, the bigger issue is the vultching. I'd like to see new ideas to help curtail the vultch. Not eliminate it, but make it riskier for those who look for their easy kills that way.
I am curious how the localized ENY would work. Honestly, I don't think it would do much against the hoards. As it happens, there are high ENY planes that work quite nicely for knocking towns down. Back in my mission joining days, I remember many many 190A8 base captures. Localized ENY might help defenders hold on, if they manage to get up in time to prevent the regular hoard rolling of a field. But I think the problem is that it is to easy for a large group to come in and simply overwhelm a base in minutes. Maybe if localized ENY affected town hardness maybe.
Even better might be for localized ENY to affect how long things such as hangars and town buildings stay down too. Even that wouldn't stop the big hoards from rolling bases.
Maybe localized ENY that lowers the radar/dar coverage lower and lower to the deck? That might help by giving warning of large NOE groups, maybe a defense can get airborn. I think there are some potentially interesting possibilities. This is my favorite idea, because it would be the hardest to game the game.