Last time around Midnight eventually recanted, agreeing that engine toggleing was no more advantageous than chopping throttle to idle (the advantage being to slow down quicker).
Its pretty easy to test, just set autospeed and compare decent rate with engine off and at idle. Same decent rate means same drag.
I doubt theres much if any difference in roll rate either.
I think it should be left like it is. Toggling allows people without a hotas setup to manipulate throttle just as quickly.