Using low level Duty Roulette as a geared 50

[Niwashi]

2) So you don't get any bonus exp as a higher lvl charater doing lower levels? I wish even though your lvl is scaled down you would still get according exp to your real level

That's what the roulette bonus is for -- to make up for the lower XP while in the dungeon with an extra XP bonus at the end of it.