Honestly, while it's certainly _easier_ with FTB, in vanilla games I've played the dragon has died far earlier than in FTB games, because when you play FTB there's a crapload of stuff you want to do first. Last time I played vanilla it was with another friend, we two played for three days and then we killed the dragon. Now, we played a lot, but we're not that awesome at MC and don't know triangulation well enough to find the stronghold with that. But the dragon is honestly quite easy, just get diamond pickaxe and enchanting table, start enchanting till you get fortune 3, get a shitload of diamonds in like an hour, make full diamond armor and enchant it a bit, same with a bow, get a few decent extended duration potions just to round things out and go kill the dragon.
The ender dragon isn't a challenge at all IMO, how long it takes to kill it seems really to just depend on how fast you can get enough ender pearls which can be pretty quick once you get a looting I or II sword.