Ours was long strided, very smooth ride, walk, trot, canter or gallop. Easily ridden for hours without you getting sore. She did the Michigan Shore-to-Shore Trail ride several times with her previous owner, camped out on the picket line. No flaky TB attitude to match the stereotype you hear about. A real lady all the way.
You have to look at the basic structure of the animal, some designs just do not add up to the most comfortable ride under saddle. How the legs are proportioned, neck, parts hung off the skeleton, angle of shoulder and hindquarters all contribute to gait comfort for the rider.
Sometimes it is the rider, lots of folks are scared to let a TB move naturally, always trying to keep them small moving. Horse argues, so rider puts more gimmick tack on to help hold them back when horse insists. Rider is just not used to covering that much ground each stride, walking or any of the TBs other gaits.
We see the same thing with our Sporthorse types, just walk away from other breeds who don't have such a big stride. Ours are half TB. I don't hold mine back to match other short-moving horses, it just makes them irritable so a fight easily develops. Some animals just can't walk together no matter how hard the rider's try. Same with many of the Gaited horses, they move BIG when gaiting, other breeds can't keep up. I personally have a hard time trying to walk with short strided people, have to take baby steps.
Get on the TB, see how he feels. Several rides are recommended, especially if your current breed moves very differently. You might need some adjustment time, to find out if horse is suitable to make you comfortable with his gaits.
Ours was off the track.. and she is really smooth! However, when she runs she tends to run at an angle.... it's quite humurous to watch from behind actually!
Just putting my 2 cents in--SIZE has a lot to do with smooth gaited as well, as I know. We've owned three TW crosses, a full-blooded TW, and (now) two KMH's. All of the TW crosses were under 15'2hh and very smooth, the full-blooded TW was 16'2hh and his running walk and his canter threw me around. Our 15'2hh KMH mare (my Avatar) is really smooth, and I cannot feel when she transitions between the walk, amble and canter. Our 16'2hh KMH throws me around, too, just like the (RIP) TW used to do, regardless of his sweet temperment, IOW he wasn't being cantancarous. And, my 15hh Arab was smooth, while my 16'2hh TB, also threw me around with his BIG gaits. ALL of the 16'2hh horses were "comfortable" according to my DH, who is 6ft5in tall.
I guess I can understand how difficult it is for "little people", aka children, to ride full-sized horses.
some appendix's/ thoroughs are easy in the saddle but In my Opinion, they are just too clunky unless at a "dead run"...Good sized horses with long strides and with good endurance just not Quick out of the hole and not able to sit on their tails in the stop....JMO
I think it really depends on the individual horse, and it's conformation. I had a 15.3 gelding. He had a very long, animated stride. I didn't realize how hard he was to sit until a friend of mine got on him. She was all over the saddle!
I wanted to add, that though, you're talking about gaits, please bear in mind that TB's have a really leggy build and they are unable to start quickly or stop quickly (like a QH slide stop.)