Not quite sure which part you're unhappy with but it seemed like at some point the negotiation became between Texan and NPC Senate, with a treaty going "through" without you/Atomic/Casey explicitly signing off on it. Don't think anyone is being clever or acting in bad faith, just that the peace was maybe a bit...steamrolled through.
I think it's fair to say the Ebonheart Treaty claims bit is...I mean, you guys are negotiating in abstracts. The Summer Islanders (and Volantenes, and Poese, and everyone) are unable to claim the vast expanses involved, so they're more areas of influence than proper colonies. Kicking Volantis "out" will just open up the eastern half to a myriad of outside influences, from Westerosi and Ghiscari to...well, anyone else remotely active or interested in the Summer Sea. Considering the utility of the Volantene trade post in Zamettar, their role in ousting the piracy in those parts and in dealing with the Brindled Men, kicking them out to make a point and allowing a power vacuum which you guys couldn't possibly fill might yield far more harm than good.