We are mostly talking Hunters here, top out at 1m, most divisions lower then that down to .5m . 8 fences per class, all related distances. Judged on style and manners, not timed. Flat classes judged on manners and style. Equitation on the rider. Much easier then Jumpers.
4 over fences and 1 flat probably is the limit for rated classes, 3’ - .75m (approx) or higher. That’s assuming the horse is fit and properly trained up for it. Meaning it only needs a few minutes on the flat and 3-4 schooling fences to warm up. Lower height divisions, the 2’6" particularly, you can probably safely add another. Below that the horse doesn’t actually jump so they can do a few more.
Some horses show a lot and/or are veterans, they don’t really jump often at home or need a bunch of jumps once at the show to practice. Other are less experienced and need more. That effects what’s a reasonable number if jumps to ask it for. So does rider ability to get prepared.
You can see example A) a seasoned pair at 3’ doing 2 classes over fences with only 20 min of flatting and 2 warm up jumps before the first class. Then putting the horse back in it’s stall for several hours then a quick warm up with 2 schooling fences and 2 more classes for a total of 4 schooling fences and 32 show jumps. Horse will not jump a course during the next week at home or on the show grounds.
Compare that to example B) a less experienced pair doing 2.6" that flats for an hour and jumps 3 rounds over a warm up course in the AM for 24 fences Needs 10 warm up fences later before first class so up to 34 fences. Then does 3 rounds for another 24 fences. 58 fences. At home rider will be doing 2 lessons a week adding another 30 jumps to whatever it dies over the weekend at the show.
So which horse jumped more? The one doing 4 classes or the one doing 3?
Thars why you cannot make assumptions about pounding based only on seeing a few show classes. You also have no idea what it did the day before or will do the day after.