In general, I'm perfectly happy with the current approach to pretenders, with the caveat that I want them to be handled with the same care in terms of scale as the rest of the line. As far as I can remember seeing in any fiction I can think of, the main '88 pretenders were all around the same size, just like the toys. Having Skullgrin tower over Bomb-Burst and Iguanus is very disappointing. I can kinda get Bludgeon, and possibly the other '89 pretenders, being a bit bigger just due to their prominence (Bludgeon, mainly), but otherwise I'd like to see them at least comparable, especially in groupings that commonly appear together. Deluxe is the sweet spot for me personally.
I guess I feel that Monstructor is a little bit different than most other pretenders. Most of them have a humanoid shell that's more memorable than their humanoid robot mode. The only exceptions I can think of are the pretender beasts (whose shells are the same animals as the robots' alt modes) and the pretender vehicles (whose shells are basically vehicles to ride around in). The beasts' shells are largely redundant, the vehicles' are basically accessories or could work as alt modes, and the rest probably work best the way they've been doing it, with the shells essentially becoming the robot mode.
The pretender monsters don't really fit any of those groupings. Their shells aren't humanoid, so really don't work as replacements for their robot modes. And while their alt modes and shells are all monsters, they aren't common for each bot like the beasts, and they're mostly very different color schemes. I think it would be hard to integrate their shells into the robots as successfully as most other modern pretenders have accomplished. Not impossible, but for example, I would prefer Monstructor keep his gold chest, rather then turn red due to using Slog's shell for his alt mode. I, for one, also found both their shells and alt modes fun and memorable. I could still be fully satisfied without the shells, but IF they were to be done as a HasLab due to being deemed infeasible as mainline releases, they're a case where I could see the shells adding to the overall package.