Offgrid,
I know those feels. I've also had lyme disease and 3 knee surgeries and some rugged medications to go with it. At 140 lb, I tend to have the same issue. I'm easily keeping up with the pack, chasing and making breakaways. I have a good jump and can tear guys legs off in a hard paceline, but that last kilometer where the pack surges I really suffer.
You can of course increase that top-end power through training, but trying to win a bunch sprint against a more powerfully built racer is just fighting your physiology.
I have some simple recommendations:
Pick races that use your strengths - more distance or more climbing
Lift weights
Strategy - work the breakaways, settle into your time-trial mode and rip chunks of time away from the peloton so that the field sprint isn't a factor in your race. Also, if you're not actively breaking away, you are never out in the wind.
Practice sprinting - you may not be able to beat captain quadricep in a sprint - but since you've made a breakaway he's probably not going to be there. You're still going to need to have a decent sprint to place well within your breakaway group.