A tailsuit made for dancing is cut differently from a normal menswear tailcoat. The armholes are higher and tighter, the shoulders are shaped and padded differently, and there are other differences besides (I'm not a tailor so I can't think of them all, but this discussion crops up from time to time so I'm a little familiar with the topic). I've never heard of anyone sucessfully modifying a menswear tailcoat for competition-style dancing.