Your assumption is that the corp or players can sit inside the plex for hours farming content. Yet the content seems to be:
Limited wave of NPCs
Limited amount of mission/site special ore with limited value
Limited time while the site is open
So why would anyone sit there for any length of time? Unless the ore is in large supply or the NPC waves keep spawning, there is no reason to sit there. Your war decced corp would accomplish nothing different than sitting in station. And the reward seen a like at best it is a skin that will flood the market so won’t be high value.
Why worry? Seems like a lot of fear over a mechanic that could be used to your advantage.
I mean say your enemies have 10 people in the site capping it out. You know the moment they leave they are either head to a gate, station, or next site. You should be able to watch them in Dscan in an interceptor and out race them to catch them at the next spot. If gate or site you are good. If they head to a station, hope they have a weapons governor the like.
Still Not seeing this as some great heaven. Yeah if it lasted a day, spawned infinite waves of decent bounty BS rats, maybe it would be an issue. Otherwise, have some faith that CCP knows what they are doing and will keep the risk in eve.