Every system can, and will, be gamed.
I'd much rather people took advantage of the existing WL system e.g. enter the WL when they're not ready because they know they'll need over an hour to be in position, meanwhile hauling their stuff to the incursion system, than have the ADHD clickfest where the first person who types an x that the FC can click on (so not automatically the first to x up, if the chat window scrolls up fast enough) gets an invite.
As Skyler Scar wrote, that also allows for forming other fleets because we know exactly who is waiting with what ships. I once spent a couple of hours doing Vanguards, which wasn't as good ISK as doing HQs but beat waiting for the gong for two hours, so even though there were people who'd rather not join the VG fleet and wait for a spot in HQ, I thought that was nice.