Sorry if this idea have already been posted before.

Just a simple suggestion: The harder the difficulty level is set, the more experience points you get, and a greater chance of getting rb's.

The harder the difficulty, the more loot will drop, and therefore a greater chance of Rainbows. As for more experience, I personally don't care.

The idea of having the same xp rate is so that you can play the game on normal or insane and still progress equally, although playing on insane would generaly take you longer since the monsters have more HP. The trade off is that for that extra effort/skill/time required you get a loot bonus, and as Necro explained, as you up your loot% you up your rbw drop chance % indirectly (i.e. rbw drop % chance stays the same but since you have more loot dropping, you have a better chance of having one of those drops be a rbw).

This update on the pts has implemented xp "cowbell" reward also, where you get +15% xp for 5 mins when you complete certain quests. You can stack this time from the bonus up to 6 times (meaning you can gain +15% extra xp for up to 30 min) - and thats a significant gain. Plus, I think you can slay more monsters on normal and gain the same amount of xp you're thinking you might gain if XP % went up on insane, since it will take you half as long to kill the same baddies on normal. With the cowbell effect in place and fighting on normal, xp bonus is great compared to what it was without it, especially testing with a lower level guy.

Higher XP with higher difficulty would lead to a lot of power-leveling, and mostly power-leveling spams. By keeping it just to Loot, we've secured us from this. And, as stated, the Cowbells work great. It really is a huge difference so when the patch is up, start doing quests!