I think it should be addressed. Being able to spin for the entire workout will only benefit you in the MTB races. During those long climbs it can be a big advantage to be able to spin up it and not completely blast your legs on the way up.
To be clear though, it is also important to be able to spin at a low cadence as well since MTBing invariably forces a low cadence in certain situations. But, it sounds like you’re already plenty strong at low cadence and have room to improve neuro-muscularly.
For my races, I always end up at a lower cadence than I started, much for the same reasons as you (well, for me it’s been high weight and low FTP ), but as my FTP has increased, I’ve been able to increase my cadence in certain situations which has helped save my legs for later… all that and I’ll also throw in a “YMMV” and throw a grain of salt on that with an N=1