How to make starter not overleveled?

[MarioMastr]

So I’m in a bit of a predicament. I’m in unova, about to fight the fourth gym, and I realise my starter is on average over TEN LEVELS HIGHER than the rest of my team. Since it starts off at a higher level than my other team members, I’m more inclined to use it, but without the newer EXP Share system, it results in ONLY my starter gaining levels. This happens when I play the other regions too. Can anyone give me advice on how to not make my team so imbalanced level-wise other than just not using the starter (if that’s a possibility)?

[Katzukiangel]

Personally I do it like this if my pokemon lv is 19 and the rest 15 I swap my 19 for a 15 and that should be until it's 19 too.
Should I ever lose an arena, I level the weakest mon until it is 1-2 levels higher, mostly against wild pokemon. 

or you just buy the new Ep Share system^^