Actually, I think that you have missed things: the
Falcon 9 can launch ~13 tonnes to leo on a reusable, but 23 tonnes to leo if f9 is expendable. IOW, it is close to the DIVH, only a fraction of the costs.
And the FH will not do a xross-over, but will still get 54+ tonnes to leo.
The falcons are currently volume limited, so supposedly, SX WAS working on new fairing. I'm sure at this moment that those ppl are working on F9's situation which appears to be their helium tank.