The first tag: you gotta consider that with Kuno that ship has sailed.
Among the first things we learn about Ryoga is that he has beef with Ranma – it takes a bit for him to fall for Akane, and the way it goes down completely blindsides Ranma (which is why he doesn't stop Akane from kissing p-chan that first time, but when kid Ryoga starts fantasizing about bathing with Akane, Ranma has enough time to react, so he fucks him up, for example) but every time Ryoga wants to confess to Akane 1. Ranma already knows Ryoga has feelings for her and what he's trying to do while she doesn't 2. the sucker keeps stuttering or making dramatic pauses or generally moving in a way that gives Ranma plenty of time to move or teleport beside him to stop it...
In Kuno's case, he's publicly showing he has feelings for Akane before we even learn his name. Akane knows Kuno likes her before she even meets Ranma because Kuno has decided to make it her problem. When Ranma first goes to school with her, he's basically learning everything he can about her world and taking notes, and Kuno essentially declares feelings for Akane before Ranma has a chance to fully understand what's going on.
Ranma watched Akane fight half the school and didn't intervene. Kuno merely challenges her and Ranma is immediately by her side, despite her showing no signs of needing any intervention, because Kuno threw a romantic little flower (the rose) while challenging her. Ranma saw the flower, Akane's popularity finally sinking in, and he's right there making his presence know (and ending up redirecting the challenge towards himself)
In fact: one of the gags with Kuno is that he's making a move before you even know what's happening. It's not just that Kuno is too unserious to pay much attention to (though he is) but that his clownery is too fast, even for Ranma. You can't stop Kuno – all you can do is be annoyed and wonder how come this motherfucker has got you again, leaving you with no choice but to step on him or sent his ass flying. He's usually managing to show up or making a move when you least expect it.
Part of his character is also to let him say something dramatic. Sometimes this is specifically designed to piss Ranma off (as in, you need to let him talk to piss Ranma off, while with Ryoga his intentions are enough to get the job done and again, Akane doesn't know how he feels) he doesn't just try to jump Akane here, which would have been enough to stop him, he also has to remark "she's not with Ranma anymore"
You also have instances like this, where Ranma is being an insufferable little bitch on purpose, pretending he's gonna leave Akane behind "to suffer" and he's still not letting Kuno get anywhere near her (this can filler under the second tag, as Ranma indeed doesn't let any guy get too close... Kuno is torture but even though Ranma is trying to mess with her, he would never mess with that... the old show fumbles this btw, it has scenes of Kuno trying shit while Ranma just watches and/or pretends to not care or doesn't even notice lmfao)
Sometimes you can even see how Kuno managing to make a move or get in Akane's space before Ranma can stop him (or before Akane herself can react) is something that legit pisses him off.
The one interesting exception (as in, manages to confess while Ranma doesn't magically show up to stop it) is Shinnosuke, but that's another post and different circumstances
