It really depends on the level of the show. I’ve found that the higher-level shows, even if they have more entries, can actually be a bit more relaxing in the under saddles since everyone is going at a similar pace, for the most part.
At lower-level shows, I’ve experienced more of a mixture of slow horses and fast-moving horses, and having some of those horses gallop up behind, or an inexperienced rider have difficulty judging how close they should pass, can cause more stress for the sensitive horses.
Of course, my observations might not apply at every show, but I’ve found they’re generally accurate when navigating different levels of horse or rider experience. Lower-level shows can of course have riders with lots of experience or who come from a program that sets them up well for riding an under saddle, and I by no means intend for this post to be bashing any level.
All that to say that the company with you in the ring can really make a difference as to whether the experience is pleasant or scary.