All they do is Ks with autos and do no damage. You ult once, it does a decent chunk of damage to one person, who's probably going to get shitton by the other 4 people anyways, so the damage you just did doesnt even matter. It has no meaningful impact. You can ash ult someone going the traditional crit route and get the same effect. Except you'll actually do a shitton of damage, and have meaningful damage.
Now don't get me wrong. I'm all for going off the beaten track for fun. But going AP ash is a serious handicap for any team that she's on. I think I'd actually prefer a 4v5. All gold she earns is wasted. All deaths she gives are to people that arent dumb enough to build stupid, who will be doing meaningful damage, consistently. 1 shot every 20seconds does almost nothing for a team fight. Hit R. congrats, you're worthless again. Vs, Hit R, now auto attack like a mother and do A LOT OF meaningful damage. Every time I see an enemy AP Ash, its a free win. I abuse them. I know how weak they are, and how much money they're worth.
Back to the 'Fun' part. If your 'Fun' actually ruins the other 9 people's fun, that's not something I support. Please consider everyone else's time and desires when you go off the beaten path.
But how is this a negative experience for 9 people you might ask? Well, there's the 4 other people that are flaming you for being worthless to boot. Then you have to consider, everyone that que's for a game mode especially URF is in some way competetive and find great joy in Winning games. Or participating in very close games. I for one LOVE close games, win or lose. But every time I see that AP ash trying to be cute, I'm going to sigh and shake my head as I tower dive her for the 40th time. Because she does no meaningful damage. Easy games aren't fun. Please stop building her stupid. I want my Fun back. And my 20 minutes of every game I have to spend rolling my eyes at this.