I did it a few times, always had a blast but competitive? Couldn’t tell you, I’m mid-pack on a good day. I never found it bothered me at all for the hard bits, but it did rip speed out of me on long lumpy bits at Ae and at innerleithen. Some races have a hardtail class, other times it seems to get forgotten (I spat the dummy a bit when UKGE promised one then couldn’t be arsed to do it) but if there is, then it tends to mean rapid mad bastards turn up on hardtails and you do even worse. I think the only race I’ve ever done that I positively would not want to do on a hardtail, is kinlochleven, it’s deadly enough on my big skills compensator and the constantly challenging surfaces would be a bit much
Mind you, I had a really kick arse hardtail, ymmv.