The
mawashi or "diaper things" are an important part of sumo and Japanese cuture...
I'd agree that sumo could benefit from grip, and would add realism. This would change the mode to a high gravity judo (hmmm, sambo?). The real kicker here is to look at sumo rules, which dictates NO attacking with the bottom of the feet (which is a fantastic tactic in Toribash sumo), and NO part may touch the ground EXCEPT the bottom of the feet (yes, NO HANDS).
I'd be all for adding grip if we could implement these rules also. I don't see this happening anytime soon, however.
Sumo is a good mode as it stands. My only complaint is DM in it at all, but I'm fracture biased anyway...
Its not accurate, it probably never will be. Get over it, practice and have fun as it is. If thats not possible, then go play Judo-DM with all the other unwashed masses.