Well went on a longish ride today.
The chain skipped a bit maybe twice during, but generally was shifting crisply, even under heavy load. FD was fixed by loosening the cable a bit.
The bike is 20+ years old but is brand new. Sat around unused for many years. I thoroughly degreased the rear cassette/freewheel/whetever and the teeth look sharp with minimal to nonexistent wear. The reason I replaced the chain in the first place is that I made the mistake of just wiping down once after cleaning and letting it airdry, creating tons of surface rust. Still salvageable, and I will scrape/rub the rust off and relube so I have a spare.
It HAS to be chain stretch. The chain felt smoother and smoother as the ride went on, or maybe the lube was more properly distributed.
The reason I tore down the derailer was that I rode it in the rain,. and the two lil pullies weren't spinning freely anymore. MUCH better now. Still nto a big fan of friction, but it does the job. Truth be told, I'm not a big gear fan. out of 6 in the rear, I use maybe like two or three at most. Maybe its because the spacing isn't large enough for me to tell a real difference from one to another..?
I will ride again when the weather clears and report my findings.