Also Ahri opts to go Aery or Comet in some matchups
just bad ahri players (people that don't know how to use the champion) use comet since this rune literally get countered by ahri's own kit
her Q will proc it on the edge so unless the enemy is trying to walk in your second Q it will miss anyway,if you charm someone he will walk out of the comet damage on his own
also aery doesn't really work with her,it may be good in low elos vs melee champions because they will let you AA them constantly without fighting back,but after the lvl 6 this rune is literally useless and pre 6 most of them could easily outrade you without electrocute (or at least survive,ahri doesn't aim to kill someone pre 6 which in fact it's the moment where she's most vulnerable,trying to have kill pressure pre 6 is useless,plus electrocute would be far better in an early game fight 2 vs 2 with your jungler)
in any case electrocute it's what most players pick so she's getting balanced around it
From the PBE changes i see that they make Electrocute like the Old Thunderlord and these champions her ok with Thunderlord.
most of them struggle in proccing electrocute
it's not like the old thunderlord,for example since you mentioned her before ahri's Q count as 1 hit so she can't hit someone 3 times with unique abilities in her standard trade pattern so the CD reduction doesn't help her at all
if she want to proc it she have to stay near her enemy and Q AA W him,but she'll end up buring all her mana so fast and her enemy will more likely countertrade 2 times harder since she's using an AA (~60 pre mitigation damage) and her W which have a laughable damage (40 + 30%AP),any other mid base rotation will outdamage this and since she needs to be near them for a while she's basically a free target
the only case where it's worth trying to proc electrocute it's when your enemy got caught in your charm so he can't fight back,but it won't happen often (basically never for higher elos)
idk if ahri will be buff-worthly after this indirect nerf but it's sure she'll end up being weaker than she currently is