The "tank structure" is the wing, and as has already been said, there is a relief valve as well as a vent, furthermore, there would have been a serious number of messages relating to low fuel pressure, which apparently did not happen.
To try and distill this matter to avoid lengthy repetition of questions answered pages ago:
1. Occams razor then suggests that unless the fuel pressure sender, EICAS, DFDR etc. was broken or incapacitated, there was sufficient fuel pressure at all relevant times.
2. If this is true, then that only leaves the supposition that unless nozzles or pipework upstream of the sender were blocked, that what was sprayed through the nozzles into both engines was something that produced less temperature/pressure (and hence less power) than what it was supposed to produce.
I do not know enough to speculate more, but I would like to ask someone with actual knowledge of the aircraft and its engines two things:
(a) Is engine fuel flow recorded? Where is the sender, and at what time interval?
(b) Is turbine inlet temperature/pressure (or similar parameter) recorded and at what interval?
If the fuel flow responded according to autothrottle and pilot inputs, yet turbine inlet temperature/pressure did not, then absent any other possible cause, what went into the engine was not pure Jet A1.
And that of course raises the question of the probability of both engines being affected virtually simultaneously.
As for EMI, I'm not an electronics person, but I would have thought that EMI capable of affecting one part of the aircraft system would also have affected a hell of a lot of other systems, and the damage would have been obvious.
Over to the speculators until we hear more from the Board.