The biggest problem with Yuumi

Is the fact that Yuumi has no experience multiplier.

Let me read you Mordekaiser's W passive. Mordekaiser gains bonus experience when killing a minion near allies equal to 50% of the experience he lost due to them being there, which totals at 82.6 / 71.73 / 66.3 / 63.04 / 60.87% (based on champions) of the minion's experience bounty.

This made it so he can continue to level up close to normally when an ally is laning with him.

Yuumi needs this, a reversal of this.

And this comes of two ways:

A. Yuumi affects the experience gain by 20%, and takes in only 80% of what her ally receives while bonded. This basically means Yuumi's ally is getting more experience at the cost of Yuumi being behind about two levels before a teamfight. Like and experience trade off.

B. Yuumi does not affect experience gain, but receives 40% of all experience and passively multiples experience based on how many levels behind she is. The ally has solo lane experience. Yuumi will always be at the least a level behind her bonded ally until level 12.