'This is her thing" is a bad argument to begin with and holds little weight.
I agree.
her time to kill is not slower than other assassins at all.
It most certainly is. Unless she's ahead already it takes her about 3-6 seconds to 100-0 someone. The reason it takes her so long is because of how much she relies on her passive AAs to get damage on an enemy champion, and because of the way her passive works, she has to literally move away from the enemy champion(or wherever they were when she procced the passive) to get the bonus damage, which takes up a lot of time.
With her ult up, which every assassin relies on anyways, she can one rotation any champ that's not a bruiser.
It depends on a lot. If she already has an established lead in lane than yes, otherwise she'll usually need two rotations from of her Q and Passive. Though there are always exceptions.
Her combo is not any more delayed than Katarina's dagger combo, and it does more damage than anything Ekko does.
You compare Akali to the AP Assassin with the most delay on their abilities, and then compare both Akali and Kat to arguably one of the weakest AP assassins atm. You're really grasping for straws with this one.
More importantly, her overbearing ability to dictate engagement makes her as much of a scourge in top lane as aatrox mid was, where the toolkit completely abuses champions and unlike ranged champs, she is way more resistant to ganks
I agree with this one as well. While she's not as bad as she once was she's still pretty frustrating to go against as a melee toplaner, but that's also a matchup thing. It's not like she counters every champion that goes top, and even if you are in an unfavorable matchup there are still things you can do to win the game. Annoying but not unwinnable.
and is one of the best scaling assassins in the game next to Zed.
I wouldn't say she scales well, at least in the way you're putting it. She does better late than most assassins due to her survivability in teamfights which is largely due to her shroud.