This is exactly the post I was coming here to make. The problem is not so much the cabin size, but the aircraft assignments. Many of my routes that used to be on 738s are now on 733, 735 (with a 20% smaller cabin) and 73Gs -- assuming they haven't been downgraded from mainline aircraft.

My connections out of IAH (or into on returns) still often have upgrade potentiality, but it has gotten remarkably hard to avoid Y -- and often a less desirable seat in Y -- on AUS-IAH or the reverse. This would be no big deal, of course, if it didn't involve boarding 25 min early; sitting on the ground/taxiing at IAH for 45-50 minutes; and then anothe 20+ minutes for taxi/deplane in AUS... it's often 2 hours on the plane for a trip that in my younger days I drove in that time (admittedly late-ish with no traffic).