As a Support/Lulu Main with 350,000+ mastery points, I can honestly and clearly say...
That with the latest change to her kit, Yuumi is now a better Lulu. And this genuinely saddens me.
Even with all the changes to the various champions, the shifts to the supporting area, Lulu has always been a pretty decent pick, because of several things. Her whimsy+ardent would give someone a MASSIVE attack speed steroid 45% + 30% = 75%, her Help Pix! passive along with ardent censer would also give their auto attacks about a rough estimate of an extra 137 magic damage as well. So she'd scale amazingly well with hyper carries like Kog Maw, Jinx, Twitch. If you are running the font of life passive, you also get to reset the ardent censer passive each time they attack the same target that you've slowed, due to them being healed by you with every auto attack. Her whimsy also was an amazing shutdown to a lot of assassins as well, due to the polymorph, and her ultimate giving and amazing amount of peel and a psudo-heal of 600 health + 50% AP. So... she has a pretty solid kit. And even though she wouldn't be the best support, her attack speed steroid would mean she was always a relatively strong pick with certain comps....
...and then came patch 9.24. Zoomies: New Effect: Now grants to 25 / 30 / 35 / 40 / 45% bonus attack speed on heal for 3 seconds.
Now there's almost no point of picking Lulu anymore. At all.
Almost everything Lulu does, Yuumi arguably does it better.
Lulu has a short ranged skillshot on her Q that fires in a straight line, slowing targets for 80% slow with a max damage of 260 but drops to 182 if it hits anything. Yuumi has a long ranged skillshot on her Q that might as well be a heat seeking missle, that may not have as big of a slow, but does a flat 275 damage with a scaling of +40% AP vs Glitterlance's 35% AP
Lulu can place Pix on a champion, adding a max of 117 magic damage to auto attacks. But that damage is useless on champions that don't auto attack, or need to auto attack. Yuumi jumps on someone giving a flat 20% Adaptive Force +33.33% bonus AD AND 20% AP
Now I will say that Whimsy does give a longer and faster movement speed buff to an ally, which does give her a point over Yuumi's Zoomies ability, however, one heals and the other doesn't heal, so I'm still going to give Yuumi a point, because at the end of the day, healing a target is better than not healing a target.
Their ultimates are where things can differ, but when you look at them both, you have to scale them based on their level of peel, their usability and their versatility.
Yuumi's Final Chapter fires 7 waves of magical energy for 3.5 seconds at a range of 1100 at a 90 second cooldown, for a 1.75 second root. Lulu's Wild Growth gives 1 ally +600 health and a 60% slowing aura for 7 seconds, which also knocks up anything 150 range from them.
In my personal opinion, Yuumi's ultimate has a wider range of effect, a longer CC and is better for both offensive and defensive plays. One can argue that Wild Growth is great for using on whoever engages in a fight, but most of the time, you want to save it for whoever will jump on your carry in a teamfight. With Yuumi, you can still use it on whoever engages in a fight and STILL jump to your carry and apply roots all in the same fight. Looking at their ultimates, most of the time it'll be Yuumi's ultimate doing far more work in a teamfight than Lulu's.
They both can use font of life and ardent censer synergies as well, with Yuumi trumping Lulu in both giving more damage and a greater heal as well.
Another thing is that Yuumi can choose to actually build 100% full AP and still give way more than Lulu, who needs to build the mandatory trifecta of
with
to remain relevant in the game, as if she builds full AP, her damage will most certainly fall off.
Whereas Yuumi will still deal a lot of damage with her Q, but can also GIVE a bunch of damage to a target as well.
In conclusion, with Yuumi receiving such a powerful change in her kit, giving her full superiority as an enchanter vs Lulu (whose last change was an okay buff to her E's shield and magic damage) who simply just comes up short in comparison to the magical kitty.
As of my writing this, Lulu certainly needs a change to stay relevant in the meta as with every buff and change to the top supports, she gets sent lower and lower down the tier list of viability.
And as a Lulu main, that really makes me a sad panda. [sg-lulu]