you have to keep in mind they're very different tail types. Veiltails, think like a sail on a boat (wind cannot go through the sail) and crowntail are like a holey sail.. So yes, they swim a bit differently because on one the water can pass through multiple points on the tail.
I can't tell you if your fish is swimming and breathing normal because I cannot see him swimming. Look at multiple videos on youtube and compare.
The fin difference is not normal, however. Is it fully formed and just smaller? Or is it broken or injury related? Again, we would need to see pictures to gauge if he's normal or not.
Did you put them in the 10g after?? Did you put the CT on the filter side? He might not be used to the current yet (Get it baffled asap). Bowser injured himself on the first day of having a low current filter (but he's better now)