I think you are being silly, tbh.
I'm not claiming to be the commercial property expert that you are. I don't think I need to be a commercial property expert of your standing to assert that a continuation of the current ban on stadia attendance would be of concern to investors in stadia development should the ban remain in place.
In fact, you go on to state that a continuation of the current ban would mean that investors wouldn't even entertain investing in stadia at all should the current ban remain in place, and I agree with you. That really is what has underpinned my argument; that stadium bans are bad news to investors in stadia!
It doesn't even have to go to the extreme of never allowing any fans in attendance ever again. Just social distancing measures have the potential to turn a stadia allowing attendances of 50,000 into attendances allowing 25,000 etc.
Admittedly, I don't know what the future holds. But it's silly for us to agree that a continual ban on stadia attendance would put an end to stadia investment, and then claim that I am being ridiculous for suggesting that there is risk in stadia investment.