my group ride is pretty spirited, I did 1 road race last year (it went very, very poorly lol), and plan on doing a couple crits and maybe a road race this year too. I'm a total numbers guy and want to have something to train towards to keep me motivated. I have a done a ton of research, and I understand all the basics, but without being able to see power numbers, I'm not sure what's the best measure of improvement.

will my HR come down? that seems like an adaptation that would happen much slower than my gain in fitness

ability to hold a higher cadence in a higher gear? sure but that seems rather unscientific relative to power output

max RPM or top "speed" at a given trainer resistance? again very unrepeatable on the road and seemingly irrelevant, although maybe the best approximate answer

I guess I'm curious if the older methodology included some elaborate or even simple algorithm that included these variables, or was training really as imprecise as it would seem? and even so, what would be the best way to measure a benchmarch with my given data points, and what are some initial guidelines for improvement using only the data I have available?