a harder capture would take more time and allow for a better window of defense ,,IMO
Which will be countered by more radical mission, i.e. bigger hordes.
It's a delicate balance... if you make base captures more difficult, chances are that the impact on gameplay will be the opposite of the intentions. When at some point the attacker figures that the only reasonable way to grab a base is a giant, annihilating suprise raid, you will get exactly this. And yes, it always can be worse than it now is

At the time we had 100% of town, no flag indicator, the battles for bases had not been longer than today, but actually shorter. They were much likely to be aborted in the face of any resistance, as the chance for a capture radically dropped if determined defenders showed up.
The other danger: Players like to capture bases. They hate to defend. Not all, but the majority. We may don't like it, but it's probably not a good idea to alienate them too much...
And I have to repeat myself, we still have a very low rate of base captures compared to the times of old.
