>But still there is problem of best player not able to gain points

The "best" player would have to fight against the players just below him to gain more than a few points, that is correct. But since this system is about comparing player strengths (aka "you are the best player - why do you want to be even better?") it's not too bad imo.

>and bad player quickly jumping to higher rank after lucky battle against strong enemy.

That is not true. In my system not only the gain and loss of the stronger player A is significantly lowered when he plays against a very low-level player B, but player B also gains/loses nearly no points.
Games between unequal opponents would basically "not" be evaluated, since both (also the low-level player!) would have nearly no gain when he defeats the stronger player
I already explained the benefits I imagine to have in this system in the post before - and I think that would at least be better than the current solution :)