This is well-reasoned and likely very similar to what I would have written prior to splurging on a pair of the Endorphins.
Some thoughts now (grain of salt = only 5ish "runs" in them on very rugged terrain similar to Hardrock ):
*They don't feel "fast" in the same sense as road supershoes, and I wouldn't remotely consider them for any race short of an ultra
*My lower legs/ankles/knees feel far less beat up after a long day on rough trails. Likely the carbon plate acting as a rock plate by default, along with the additional stack height
*The midsole is not "mushy" at all - while it's plenty protective and has a bit of rebound, it's actually firmer than my other Saucony's (Xodus)
*Actually lighter than the Xodus
*No idea if I can crank them up to "race" speed, even ultra race speed. Of course mtn ultra race speeds are glacial on average, but you still want to be able to boogie on smoother flat sections and downhills. While they're a bit clunky feeling on flats, they do feel like they could go downhill well due to the extra support and stack (haven't really it tried yet though)
*Bought them not only for the rotation but possibly also for use in an upcoming mtn ultra. Still on the fence between them and the Xodus
*Regardless of all the above, they're definitely a great Hoka alternative for those who don't fit Hokas well. Road supershoe comparable, maybe not so much