There are two different ways of looking at this, but neither of them supports your case.
Either:
1) There is no way to know how many innings Joss would have thrown in a different era, and thus SOM's treatment of that question is no more or less valid than any other; or
2) (and I personally think this is 99.9% likely, which is good enough for me personally, but it's ultimately unprovable...) Joss simply would not have been able to complete virtually every game in a non-deadball era, and therefore if you're not playing a deadball replay, which we're not, SOM is obligated to ensure that he does not do something impossible like that.
The reason you don't have the option to put together a team that plays as if it were the deadball era is because the game is not about choosing an era for your team to play in. It is about choosing players from all eras, who come together to play in a "mixed" era.