I would stop at 45.
I second that. There's really no reason in the game yet to go past 45.
Stay at 45 and be happy, unless you're meta and do 70k dmg.
There is no reason to stay at 45. The world doesn't really get any harder past 45 or even 50. I'm at AR52 now and I don't notice much difference from when I was 44, 45, or 46. In general the difficulty of the open world is very easy, but the last tier of stuff like Stormterror and Tartaglia unlocks at 50 so you're missing out on that staying at 45. The difficulty of instances is set by you, when you choose the level, and is not impacted by world level. Technically at 55 you finally unlock a guaranteed gold artifact drop from world bosses but that's a very long grind to get there.