Taking away the AP scaling from their sustained damage spells just makes them 100% unviable in ranked. Your game plan can't be just to hope to snowball super hard and one shot people. These changes kill their AP path rather than buff it.
ap shyvanna has always been absolute fucking trash and if youve ever played it you trolled your team mates hard af
Looking at these numbers,
Building AP for 2% targets' max health per 100 ability power
when the base is,
15 / 30 / 45 / 60 / 75 (+ 4 / 5 / 6 / 7 / 8% of target's maximum health)
CDR is just infinitly better for damage on just the W. That scaling is garbage compared to that base damage. Who in high elo even makes any AP on zac.
AP zac isnt alive to be killed.
I'd argue that these changes let you try AP assassin ZAC moreso than your proposed, current itteration of "AP bruiser but less rotations than tank cuz he isnt as tanky and he is missing cdr so he isnt as damage-y but he also smaller so he hits less people and he doesnt live as long so less damage again Zac"
I think that's the point. Riot shoved Zac's scaling to his engage spells, to keep ARAM Zac alive, but have a personal problem with AP Zac Jungle apparently
It wasn't the damage of Zac's W that made him viable.....
They don't make the champions worse per say. They just make it so you have to change your play style to use them better. The only thing unviable is the people that can't adjust.
I dont know if you know but shyv q has plenty sustain with 
and lethal tempo.
and 
.
How to kill the only ap that this tank sometime build
