I don't think Accelerator can beat Tetsuo. Their level is pretty close but Tetsuo is stronger IMO. Anyway, herald level characters and above could beat him with relative ease to effortlessly. Magneto in his stronger incarnations is probably the weakest character I can think of who could beat Tetsuo for sure, partly because his defense and scope exceed Tetsuo's by a moderate margin and he is immune to telepathy with his helmet. Also he could disperse Tetsuo which would likely bypass his defenses.