Merit points can be spent on something else than just build and improving our character's combat abilities.

For example, getting merit points for a glamor stuff? Or just reward merit points for a certain amount of exp scaling on the job's level. But merit points will cap at a certain number, like 10 or something.

1 merit = 2% of exp.
So at maximum, a job can instantly get 20% exp.

In order to get merit points, you'll have to run roulette and each day there is a cap on merit points. Make the cap small but reasonable. Each day, we have 6 (not counting PvP) roulettes to do. One roulette = one merit point. We do dailies with our 60, that's 6 points already and you're still doing the same things but now you get more from it.

20% exp for a job instantly is something not to be taken lightly..... especially when the job is post-50.