This is an interesting question- I’d feel a little head-scratchy about a pro showing in a 2’ class because: why? A kid or a newbie ammy might need a puddle jumper class to gain confidence, but if a horse was doing that with a pro because it couldn’t handle anything higher I would question the training or the trainer.
I’m not a pro but I’ve never shown in a jumper class below 2’6", and that height was when I was first showing my 4 year old. He’d been to a couple of dressage shows with the trainer who helped me break him, and I dragged him along to hack around the grounds when I showed my other horse. But, we didn’t bother showing him over fences until he was happy plopping around a 2’6" course. Every other green horse I’ve introduced to the jumpers has done 2’6"-2’9" at first, and then gone up. If I had one that couldn’t deal with jumping at least that height I’d re-evaluate what we were doing in its training. I don’t see the utility in showing over tiny courses for a normal, fit young horse. Not to be an old person but when I was a kid the hunters started at 3’, and the jumpers at 3’6", and everyone survived.
My friend who trains eventers and event horses sends her clients in as low as they need, but the horses she takes in on training or her own young ones start with her at BN (2’7"), generally. It’s a nice, easy height for them, she’s an excellent rider, and she’s done the prep work so they have good outings. And that is a full event, with all three phases! Any horse that cannot handle 2’6" or higher in the jumper ring even with a pro would make me wonder about it and/or the trainer.