Here we go again.
I am with STF, unless a horse is bred for a discipline, his suitability for that discipline is limited. There will be surprises, and lines of horses that differ from the original intention of the breed. Breeding itself is generalization. When a person decides to breed a Belgian, what do they have in mind? If somewhere in the equation has dressage, then yes the suitability is high.
This applies to any breed, any discipline.
I have only worked with 2 Belgian crosses. I cannot stand their personalities. Very head strong, and stubborn, not smart. Laterally stiff like most other drafts crosses. However, both horses are bomb proof, tough (can carry quite a bit of weight and easy keepers), and steady hard workers… they have quite some opinions so a little bad riding doesn’t hurt them as they will find ways to deal with it (unfortunately good riding doesn’t necessarily improve them a great deal either). Both I rode are crossed with QH. One of them did eventually become a really good beginner schoolie.
2 horses doesn’t mean anything… but they sure made an impression on me.
Remember suitability usually means ease of use. Sure you can use a stock pot to fry eggs. But if you fry a lot of eggs, why use a stock pot… but it will make sense if you make a lot of stock, and seldom eggs. So it depends on the rider’s goals and ability, and access to suitable training.
To reiterate, I have a TB and a Clyde cross. Both of them are limited in dressage… I believe neither of them can sustain a lot of collected work, nor would the collected work be of high quality.