I agree rix, in real world yes they would be limited, but since there is no limit how many troops you can have only your credit card limit.
any top coalition have few billion defense that's given, but what stopping them to have 10bil or more? if some players coin really hard.
my point is that if they are know that pantheons are spawning, yes they have many active players and will be waiting, but if they have to capture lets say 15-20 patheons at same time it create really stress on them, give chance to others to maybe capture one and reinforce it.(time will tell if they can actually hold it) but if only few pantheons release these top coalitions will stack them up with hundreds of millions in 2-5minutes and game over for everybody else.
or use their sister coas to each capture 1 pantheon for them, like lost souls, did they ever capture their own pantheon? not sure which drugs they giving to their sister coas, but since like forever others capturing pans for them. but still if there is 100 pantheons spawning, chances are new coalitions can capture one.
it is true u can try to take pan from top coa, but they don't take it well... they might give people some slack if they took pantheon from xerxes, but not from them.
as rix pointed out, it would cost them lots of offense to capture it, but then no amount of defense will hold it as they will retaliate and they will be out for blood.
Reason why top coas are feared is not their defense, but people who will downgrade capital and raid cities over and over again with hundreds of million armies in size.
so I repeat again, more pantheons spawned at same time, creates stir, higher chances for average coas to grab pantheon and it creates quite amount of pressure to top coas. if pans are released in small numbers top coas will be well prepared and will dominate map even more. Diversity is good thing, not handful of coalitions dominate everything