I don't think you're right, vexing, and you certainly are not about the Seaport/Harbor issue. Harbor and Seaport aren't the same tech levels and aren't comparable. Otherwise, you'd also have to complain the Hospital is significantly worse than the Granary.
Not that I'm saying improving the current Seaport would be wrong, mind you. Do recall, however, that they serve different purposes. Also, gold upkeep is higher on the Harbor.
I do believe I'm correct about the tanks. It's simply that you get a bonus from having aluminium access as well as being very technologically advanced. Having teched Lasers mean you are likely going the domination route (rather than aiming for ie Globalization) and so should give you an advantage - much like the GDR (which, by the way, being a super unit and all, they will surely never have at the same cost as the Armor).
Nope, you can be perfectly certain the late-game production costs are precisely how they wanted them. I say this because they noted having given special attention to the Nuclear/Solar plants which means they no doubt compared their costs to all their contemporaries. Whether they made the right choices is a different matter - and the Seaport remains questionable.