It shouldn't be the responsibility of a user to have to defend the same 2 plays over and over in a "sim" dynasty. That is not sim football. It doesn't matter if it is stoppable or not, you shouldn't have to deal with it and if you're trying to run a sim dynasty, that type of football has no place.
As for stopping it, your situation sounds a little different. He came out in the same defense every play, so you ran a combo of the same plays over and over to beat it. If a defense is forcing you to doing something, then do it. In my case, there are times when I'll be in my spread option and run HB Dive out of 4WR Trio or Spread Flex 10 times in a row because people want to sit in Cover 2 and Press. If you're reacting to a defensive set, do whatever you need to do.
But if your offense consists of Power I toss and 5WR Slants, you're up to no good. It is impossible to stop 5WR slants against even a slightly competent player. Bring pressure, they are quick to the flat. Sit in zone, they wait for the slants to find the open area because there is no pressure. Go straight man, they just hot route that inside slot to a slant against a LB and you're finished. That doesn't even take into account when you play a team with a scramble threat at QB. Yeah, you can probably pick up tendencies and stop it a few times, but you have to stop it 3 (or 4) times in a row, which is pretty damn tough.
Can't blame him for booting him. That said, I would like my chances playing someone like that because I trust my ability to adjust and pick up on their tendencies.