Hope you don't mind an AA puke chiming in, but a few months ago I flew with an FO that came over after 4 years at JetBlue. That person lived in NYC, and what you're talking about is exactly what they were chasing. When you combine NYC being crazy junior with widebody slots grabbing a certain percentage of the list, it doesn't take long to get senior in the right seat of a narrowbody. A quick look shows 3.5 years gets you into the top 20% as a 737 FO. Guessing it's similar or better at United or Delta.

That said, I've got 8 years on property and can't hold weekends off in the left seat unless I bid reserve. Covid really stagnated us on the CA side. We just had a few bids with a large number of upgrades, so once those guys hit the line hopefully things will start moving again.