Also, I think the writers will tell you it isn't the Aryans that are the ones bringing Walt down. It's his own ego/hubris/incredibly awful decision making.
Edit: Also the Sopranos was about a professional criminal organization. The whole characterization of this show has been about how amateur of an operation Walt has. An organized mob is of course going to have natural, sustainable, long term rivalries. A chemistry teacher turned meth cook who just tries to overrun everyone he comes in contact can only get away with it for so long. He hasn't been in the game long enough to actual develop any actual rivalries.