UD - you recommended a 9x14x22 bag. The aeronaut 45. Nice bag. Well made.
Soft sided. No wheels.
But still 9x14x22.
Only times, in over a million miles as a passenger, yes, over a million, not flying as crew, that I've absolutely had to gate check a bag of that size is on an EMB-145, and flying into Poznan, Poland on one of the smaller Euro carriers. Now, I gate check my bag on RJs out of courtesy to others.
So, you and I are recommending the same size bag, and you're suggesting that the hard bag won't be allowed, but the soft one will?
Since the OP is traveling in the US, the allowable/fit issue becomes moot. Soft sided vs. hard is an interesting debate on what survives gate checking, because he will still have to gate check the aeronaut on smaller airplanes. Unless he's a total douche that attempts to takes up the whole overhead on a CRJ, but that's another subject. Most FAs at regional airlines, won't allow a bag that big, be they backpacks, soft side, whatever.
They know.
And the only criterion remaining is: sling it over your shoulder, or roll it.