I basically agree with everyone else here that it’s hard for us strangers on the bb to tell you exactly why your pro rides aren’t working, but they clearly aren’t.
I just want to add one more possibility to the table about potential physical aspects (in addition to tack fit and doing too much, which have already been mentioned) based on some personal experience.
When I groomed, one winter the barn had a young horse who was mainly mine to ride, but a pro did all his jumping and an occasional flat school, though usually they just hopped on after I had flatted or had a nice long hack from farm to show. I loved the horse and was super grateful for the opportunity, but he did often make me feel extra-mediocre in my riding. He could be a little fresh, but mostly just was a big lanky baby I struggled to balance. I learned lots of warm-up and stretchy trotting improved my chances for eventually having success at the balancing, half halts, and a manageable canter.
After returning north in spring, horse went to pro’s facility full time for about a month, then back to our barn. I went to groom and tack up for the first time, and was shocked to find how sensitive he was over his back. The pro’s saddle wasn’t new to him, and didn’t appear to be horribly off in fit (to this layperson’s eye). The next week we went to a show. I tacked up and handwalked him the 300 yards to the ring. Pro gets on, trots a couple of laps, picks up a canter. Does a bit, jumps a warm-up fence, then goes in the ring to school. Comes out, hops off. It’s all over in 15 or 20 minutes, and it suddenly dawned on me… if all the rides in the past month have been remotely like this, then the horse is probably sore from lack of warm-up and cool-down.
Now, without a doubt the pro was a way stronger rider than me. So, not only could they generally get more out of the horse, but they could get it done a lot more efficiently than me. And yet, even if this work is technically correct and should build the horse up, done too much + too fast, it can really be a net detriment physically.
Looking around now, I see this is a pretty common thing. Pros can get on and get a horse going a certain way quickly, and often don’t think about whether they should. Often it’s because they are super busy… a long ride list at home, or juggling a string and multiple rings at the show. Sometimes it’s just because their personality is super driven and focused, so they ride that way too – the same traits that make them good in the show ring make it hard for them to toodle around on a long rein. Owners tend to naturally take things slower and take more breaks if left to their own devices… sometimes that’s not a bad thing. In fact, I would say the ws/groom/fellow-client rides (that often get lambasted on this board) can provide a much needed balance between true pro rides for a horse in a full-time program (of course, only with full disclosure, approval, and appropriate billing to the client).
Anyway, that turned into another of my long rambles. But my conclusion is the same as most of the other posts on this thread… if you want to know for sure why it’s not working, you’re going to actually have to watch the pro ride. If you just want to stop being frustrated and accept it’s not working, then move on.