Just a few examples:
**Riven:** probably her best keystone right now is fervor, she likes thunderlords against squishy teams but in tank matchups she definitely deals way more damage using fervor, simply because she autoattacks between all of her abilities so she can stack it fast and deal more damage than with a single tld proc. Furthermore she wants pure ad because of the ability damage and extra damage on her autoattacks between them. She doesn't profit from attack speed as well as she does from pure AD, especially once she gets some cdr so her abilities become spammable. Her best keystone would be probably press the attack which outclasses electrocute for her but this way she has to choose between the lack of ad or the lack of stacking damage on autos. Meanwhile Fiora wants attack speed and wants press the attack, it used to be a kinda even matchup and Fiora will definitely stomp it because of the better runes.
**Jhin:** He definitely doesn't want attack speed over AD in the early game, but his best keystone is warlords, aka fleet footwork. Which means he either takes electrocute for the early game which doesn't scale well, or gives up his early game power because he has to take attack speed.
**Miss Fortune:** She wants pure ad over attack speed as well. She doesn't even have a keystone that would proc on her ult now. Maybe PTA does, I don't know, but this way the same happens to her as to Jhin. These 2 champs are meant to be lane bullies and having their early games indirectly nerfed is a big issue.
I can't think about more champions right now but I'm pretty sure there are many more, especially between toplaners. We should be able to select what kind of basestats we want.