Which philosophy is it you want them to follow? One amp, not two done badly? Don't even offer something like Full-Res IR if it won't fit? Or, like reverb, allow better with extremely reduced layouts, OK with a couple more blocks or economical and still a few more blocks? Currently it's basically the first, they crammed what they could in and future developments might allow improvement.
Fractal is all about the quality of the sound. Even the Economy reverb is very good and in a band setting in a normal venue is indistinguishable from Normal. The single amp block is to allow the expected amp modeling quality, while leaving room over for the reverb modeling because they run in the same chip. There's not enough CPU available for two amps and the days of allowing two but with reduced quality are gone; They've been there and done that. And, Full-Res IRs require more CPU and memory than the Ultra-Res, on a device that's already constrained, so that was a non-starter; That they managed to get the FX3 Mk I to handle them was a real chore and great surprise to the community, and it has about 4x the CPU power and twice the user cab slots of the FM3.
Fractal has done a great job
positioning the three units, and they're not frivolously picking and choosing features. They fit in what they can given the hardware's capabilities, and then start optimizing to make even more fit in.