It's not a failure of imagination. It's simply not very plausible given the circumstances and time frame that the characters on earth would have the opportunity to rendezvous with the Normandy, which is supposedly supporting the space battle.The problem I have with people complaining about this is that there are SO many plausible scenarios in which this could easily be explained.
But fret not, it has been officially stated that these holes shall be filled and so nobody will have to use their imaginations to fill them:
Although given the number of inconsistencies with the ending, that one's pretty minor. Go get the "perfect" ending and you'll see quite a jarring one.