If you’re serious about XC racing, I think you need a bike with a remote and a lockout.
I rode a 40min smooth singletrack climb the other day on my new gravel bike. I was 1.5 mins faster vs. my best time on my full sus MTB (it has a “firm” mode, but not lockout on the shock). Tires are also different, but I suspect a bigger portion of the time saved was from better pedaling efficiency.