Wow. Looks like you did a lot of work on that Sherline mill. I have a Sherline 5400, just like that one. I have to say that I'm very happy with it, but do some similar reservations with it. It's a light-duty machine, very precise and accurate, and great for learning manual machining at a reasonable cost. All of their accessories are basically scaled down traditional Bridgeport-style tooling and fixturing. Not a bad thing at all. Also it's DC motor is decent, especially at the low-range to cut harder materials like steel. (The motor is more adept with their micro lathe, rather than the mill though.)
But the mill isn't made for CNC. The lead screws always have about 0.001-0.003" of backlash and the aluminum ways can wear quickly with constant CNC tool paths, if you're not diligent with oiling everything all of the time. With traditional gibs, you have to frequently check them to make sure they are tight and don't have any play, because they also wear quickly.
I agree though with your assessment. The linear bearings and timing belt drives that the Nomad uses is the way to go with modern-day light-duty CNCing. No backlash. Virtually no wear. And still very accurate.