I have heard that the use of protestant ministers in place of clergy was briefly accepted for a time and then immediately condemned. You cannot hang doctrine on practices that have not endured where those practices ceased due to condemnation of them (arguments can be made when practices simply fall into disuse).
Regardless of that, the easy counter to that argument is that whatever the practice in England, the Lambeth Quadrilateral supercedes that as a clearly articulated policy of TEC. Reunion with other traditions/communions (including full communion relationships) is based on the Labeth Quadrilateral which includes in its criteria the historic episcopate.
Again with ELCA General Convention firmly stated that entering into full communion with ELCA would violate the Lambeth Quadrilateral, so the "compromise" was to suspend it, vote to enter into full communion, restore the Lambeth Quadrilateral and then there was the whole proposal that all ELCA bishops would henceforth be consecrated by Anglican and Lutheran bishops to, effectively, restore the apostolic succession. Then various ELCA bishops refused and it all fell apart, but that was the plan.
It's an awful lot of mental gymnastics to try and make this relationship fit, no matter how you look at it, without substantial change in the UMC?
Here's a new question then: if these full communion relationships are so important as to (and I think everyone would generally agree to this) violate the Lambeth Quadrilateral, is it time for TEC to just abandon the Lambeth Quadrilateral as an instrument of unity? Acknowledge that it no longer represents the criteria for full communion and that they no longer believe its beliefs to be essential to unity?