Everything you're thinking there is the exact same stuff that popped up in my mind when I heard it. 2K wasn't worried about legality though. They were worried about leverage. What was explained to me later on by Anthony Chau was this:
The license was due to expire soon and they wanted to get back into the NFL game BADLY. 2K's fear was that if people can create a league that looks exactly like the NFL, it would make the NFL license less valuable. This devaluation would of course make the NFL angry and be less likely to cut a deal with 2K for the license when it became available.
Now, some of that is a valid concern. The problem is, the idea that they had a real shot at the license is the critical issue. I mean, there is nothing wrong with holding out a little for a possibility, but did anyone REALLY think EA/NFL wouldn't renew? I sure didn't. I was confidently certain that they would if EA was willing to put up the money. The NFL had no motivation to sign with anyone else, because they were getting their money (and a lot of it) direct from one source. EA of course did not want anymore NFL competition on the market (I love you guys over there, but we gotta put the cards on the table). It was a perfect set up for both parties.
Now, as far as having a deep editor that would allow someone to recreate the NFL. Legally, a company would not have any strong grounds to sue BackBreaker for that. The assets used to re-create are all in the hands of the end user. The company can't be sued based solely on what the end user does to re-create the NFL.
The only place BB would have legal trouble is if they openly encouraged users--in specifically certain terms--to re-create the NFL, which they wouldn't be dumb enough to do. Or, if they began hosting those assets created by the end user, and even then it would be a thin case because of the implied responsibility taken on by the end user. It would be one of those cases where they file the suit and it likely never goes to trial.