Mike Goldberg pointed this out last night (I'm paraphrasing here): "On average, Chuck spends only 13 seconds on his back when taken down."
So, it actually sounds like the game did a fairly accurate job portraying the fact that A) Chuck is hard to take down and B) it's hard to keep Chuck down once you get him there.
Obviously, if the submission attempts are still a struggle with every fighter, then it's an issue but with the 2 guys you have at your disposal, I'd say it sounds about right.

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