It is literally no more of a problem than the fact that a level 20 paladin will have the same bonus as a level 2 Paladin if they both have 28 charisma.
Which is to say...
It is not a problem in the least.
You want a better Divine Grace? Take more levels of Paladin AND increase your Charisma. Simple as that.
Believe me, you don't need it. A +8 bonus is more than a toon without 2 levels of Paladin is going to get!
Might as well start complaining that none of the other classes get a Monk's excellent save growth just by taking two levels of Monk.