I wouldn't be keen on jumping a full draft, it just isn't at all what their bodies were meant to do. That said, I have seen a number of Clydes do it well - and many Clyde crosses that are excellent jumpers. Personally, I would be concerned about their joints over time, while they are often proportionate for bone-body mass they are a lot of mass.
I do ride my Clydesdale mare, we work on dressage, and we work according to what SHE can do. Nothing at all wrong with that, and yes, it is very possible to find full Clydesdales that do very well in dressage - it's about looking for the conformation traits that give ability in that kind of work (Clydes and Shires seem to have numerous individuals that are more "sporty" and why their outcrosses tend to be very popular).
I haven't had my mare out to shows yet, but she has done a few clinics, the coaches all quite admired her way of going, and loved her willingness to try, nobody watching actually came out and said the words "elephant in a tutu" either
. ... And while she is not one of those Clydesdales that will move onto higher levels of dressage work, I don't need nor expect her to... We can still spend a lifetime getting the "little stuff" right.
(Just for information, I have also done some harness work with her... She just isn't a big fan. I'll likely not ever take up driving as a full time venture, with any horse, but it is kind of a neat thing to learn too - and it definitely seems to be one of those things most horses can benefit from)