Things I’ve noticed at XC races in the last couple of years:
29 inches is by far the most popular choice of wheel size.
Anyone still running a 26er will insist their bike allows them to make up ground in the twisty bits over the 29ers. But when pushed they’ll reluctantly admit they have never actually ridden a 29er.
The only riders on 27.5ers are sponsored. No-one actually buys them.
There’s always a super fit rider on a fat bike who passes you at warp speed and throws it round like it weighs nothing.
When you catch up with the fat bike rider at the end of the race you realise his bike really does weigh nothing and probably cost more than the deposit you put down on your house.
Some people REALLY don’t like being beaten in a sprint to the finish line by a singlespeed.