I disliked that Ironhide/Ratchet mold from the beginning, but over times it just looks worse and worse knowing what is possible with these figures. I'm pretty excited for the FansToys versions coming out.
IMHO, Ironhide and Ratchet would benefit from being a "leader class" set. That way you could have an interesting robot mode, but enough left over to make some kind of diorama add on. Consider WFC/Siege Astrotrain. They needed a "caboose" and they needed to cut off filler from the robot mode, so they created some kind of launching pad system as a compromise. I'm not a fan of it, but they only had so much space and size to work with and they were probably stuck. Whereas Studio Series Ultra Magnus, he was so big, and there was enough budget, you could fuse his trailer into his robot mode without forcing him into an armor situation that detaches.
The problem then is scaling to the original cartoon. I think Ratchet has more options, since he's a medic, and you can turn his back end/diorama end into a repair bay. That makes sense for the character. But Ironhide, he's another soldier, probably 2nd or 3rd in command. In essence, while its too late now, if you switched Wheeljack and Ironhide, that might make more sense. If Ironhide had Wheeljack's backstory, then you could use his back end for some kind of mechanical bay, etc.
I am curious about the original line. I.E. if they used tooling for other car sets/car models at the time to save on R&D, and that made it easier to make certain kinds of cars over others.
At this point, it looks like the only compromise they can make now, on a budget, is to turn the top of the van into a shield, i.e. the DK-2 Guard. I agree with you, the robot theme looks a bit odd. The only mainline I've seen so far that did a good job of hiding bulk was the Titans Return line. The necessity of a headmaster and a cockpit/canopy forced a lot of interesting workarounds IMHO.