most of us haven['t beaten G maps yet. Players that have played from the first day haven't yet. Pretty much the only peeople that have cleared all g maps are people that invested a lot of money in the game and have a number of blacks and awakened units. For example the only g map i've 3starred on the dailies is the skyfallen gift one , and that's because my archers are actually great , with stuff like awakened spica and nanaly and bashira , and perfect solano , and awakened healers and so on. You get the point.
As for the story maps...well they will always be there. You don't actually need to rush to finish them. When i started i think it took me quite some time till i managed to get a team good enough to beat imortal beast