Unfortunately, the term F2 has been manipulated over the years, or at the very least used incorrectly, and it often leads to this kind of confusion.

The vigor is definitely not gone. If it was the consistency of the calf crop would be noticeable higher. In general, heterosis charts in the opposite direction of purity. It's generally accepted that it takes 7 generations to create or eliminate a breed. Each step would display the next level of heterosis. In the real world we know single location genes out last those 7 crosses much more often than originally assumed, so there's no way we can confidently say heterosis is gone even at that point.

As someone else mentioned, considering what modern Simmentals are you would have to be careful about applying absolutes to them as we can't really assume they are a pure source of differing genetics when compared to Angus.