How can you express the disagreement without coming across as arrogant or condescending?
You can't, so you don't.
I'm in a similar situation where I am required to relocate every 2-4 years. Not only does this mean I will likely not have continuity of training, I will also likely never achieve dan ranking. Am I worried about that? Not really.
Every instructor, no matter what his connection to "big time aikido" might be, has something to teach you, even if it's how not to do something. However, if you go into every new dojo judging it by all the previous dojos plus your own experience, chances are you'll miss it. Completely. As one of my former instructors used to say, you have to go into each new place with an empty cup.
I would suggest that if you are that unhappy with the local aikido dojo where you are, then take that time to crosstrain in something else. Try kendo, iaido, BJJ, or kung fu perhaps. Currently I am two hours away from the closest decent aikido dojo. While I occasionally put on an appearance there, I am also enjoying the chance to work with an extraordinary goju-ryu instructor.
Good luck to you.