In fairness, considering that the very idea of a Mass Effect Field makes absolutely no sense in physics I think we don't really have to worry too much about it being hard sci-fi. And Lucky does have a point, while until now you've always needed two relays for travel, we know there won't be any more so there has to be a way for them to cross the insurmountable space between galaxies. So if we somehow get shot across space by a Mass Relay Cannon then frankly I'll accept that completely happily.
I mean, conventional FTL in the game would just be far too slow. Compared to the size if Galaxies, the speed of light is absolutely fuck all. Considering that it would take ~100,000 years to cross it at the speed if light... (And it's not even a particularly big Galaxy!!!)