That's a good point. My impressions are just from the first battle wave plus the first attempt at resupply on both sides, which in two instances happened at the same time (which I'm sure is what is making the map feel barren). I bet you're exactly right that as the landscape changes and we establish our respective objectives, the missions will take a nice new "shape." I'll have to let one run for a few hours and see how it looks.
I really really like the idea of Packets for both OPCOMS, but I've tried both Constant and Packets with varying degrees of success - of course this "split battlefield" thing I'm sure is more pronounced with Packets, especially if both sides are equally strong in profiles and ability.
In brief testing, Constant reinforcements seems to shift the evenness of the battlefield quite a bit in the early stages. If one side gets replenished while the other quite hasn't, when the replenished side gets back to full strength they just goes on a tare and decimate the opposing side for a bit.
Of course, that probably isn't a bad thing because that's the way war is; one side has the edge until suddenly they don't anymore. I'll have to spend more time with each option to see which is right for me. :)
I'm loving it though. One of the missions is vanilla(ish) on Altis and I forget how great that map is to explore! It's awesome.
All in all I think I'd appreciate it if the OPCOM cycles happened faster, but I also don't mind things being "slow" and just exploring - especially if cycling OPCOM would hurt performance (I can't see how it wouldn't. It definitely would not be worth the trade off if that's the case).