I get that Yuumi is supposed to be a scaling enchanter pick with early game as one of her weaknesses, but as of right now Yuumi struggles insanely hard to win lane 2v2. Due to the removal of the bonus damage on autos from Spellthiefs, Yuumi's laning is even weaker because she gets outtraded by every other enchanter or mage support to the point where it's more efficient to avoid detaching at all except for getting the shield from time to time or to help with some tiny dps at all ins.
Before, Yuumi was able to apply a bunch of pressure onto the enemy adc with constantly poking with autos and then W-ing back to the allied ad but now even that is just not practical anymore. Her laning phase just feels like a 'hugging tower to stay alive'-simulator.
With 9.23, Yuumi's win rate has hit a new low of 37%. I really think she needs a little buff onto her passive, like maybe giving her the bonus mana back, so she can't get dominated in lane so easily and transition into midgame more healthily. Yuumi also suffered from the gutting of Presence of Mind and the indirect Cut Down nerf, since Spellthiefs grants extra health now.