You're forgetting that a connection between man and spren doesn't necessarily mean man and honorspren. It's been stated that it could be another type of spren, maybe flame, rot, death, wind etc... So if that is the case who know what other kind of powers there could be. We've seen a surgebinders powers as far as windrunning used by Kaladin and Szeth, the lashing and so on but I don't think we've seen everything yet. The powers that Kaladin and Szeth are almost unheard of and not much is known. Only one character had even a slight idea of what Kaladin was doing and he came from a family who was passing the knowledge down through the generations. As far as Szeth having his powers through his oathstone I'm not so sure about that. He has never actually had it in his possession, only his masters have. Now he could be connected to it and have powers that way, but it sounds like that would be a first as every fabrial or magical type item, from shards to lanterns, have had to be touched in some way to be manipulated.