[Nick Beale]

It seems to me that, all things being equal, a fighter-bomber that spends less time flying its mission (i.e. one that can make the round trip to the target faster) ought to have an improved chance of survival.

So far so good - a fast jet has potential in the role. But, if you are then so concerned to preserve the jet's secrets that you only allow it to bomb from 4000 metres or above (without a bombsight), as was done with the Me 262, then you have just squandered that potential - your aircraft may survive but it won't often hit any tactical target, so you may as well leave it on the ground and save the fuel.