Zur is only linear if you feel a need to build and play it optimally. I haven't played him, but I've played commanders that can tutor a couple times, and it is possible to self-impose variety, either by choosing to fetch different cards each time, or build a deck that doesn't have a clear path. With Zur, you could put in a bunch of cards that only really work depending on your opponents, like token hosers and graveyard hate and color specific effects and such. Then you could play some group hug stuff, so your opponents get lots of stuff going on for you to react to. The early game could be group hug, and then you can scout out your opponents' decks and try to figure out the puzzle of how to shut down each strategy and take over the game. It'll mean sometimes you draw completely dead cards, but it'll also mean that each game will feel like a new puzzle to figure out. It may not be the winningest Zur deck, but it won't get boring very fast.
K'rrik can definitely be built as a goodstuff commander. I'm not a big goodstuff fan, but, if I was building mono-black goodstuff, he'd be towards the top of my list of potential commanders.