What's the deal with the Keyboard?

[Sephiroth]

So I'm playing through KH2 Final Mix (gameplay and worlds are great, story is still very ehh) and I've started to become a little confused about the keyblade.

So as I understand it, the keyblade chose Sora in KH1 because he had such a strong good heart, and Riku was passed over because he chose the Darkness where Sora fought against it (as seen when darkness takes Destiny Island in KH1). OK all fine so far.

Then actually Riku CAN weild a keyblade as seen in KH1 at Hollow Bastion because...why? His heart is stronger at the time apparently but what about him being knee deep in darkness? Then Kairi also gets a keyblade randomly in KH2, handed over by Riku who had it for some reason but who chose not to use it for some reason.

Then Roxas can use it and it's like wtf, I thought he didn't even have a heart. I know he's Soras nobody but can the blade not tell the difference? Then I hear there's a prequel where there's like 3 or 4 keyblade holders or something, even though some of them aren't really on the side of light, then there was a war where a whole bunch of keyblades were used?

So how come the keyblade has gone from a powerful, special and unique weapon to one where everyone and their mothers is using one? It makes me wonder why the hell Donald and Goofy don't get one since they've shown to be strong loyal and pure of heart, probably moreso than most of the actual wielders except maybe Sora and King Mickey.

I dunno, I always though the keyblade was kinda cool but they're getting thrown around like it's no big deal really, and not really explaining why anymore.

EDIT: ach! Can someone change the thread title to what it's obviously supposed to be? Creating threads on my phone is such a ball ache.

To shorten the entire thing:

1. Riku was chosen to wield the Keyblade of the Realm of Light. Riku was no longer worthy. But he is a Chosen One nonetheless.
Riku found his own way of Living. He did not push away Darkness but dealt with it and learned to live in Twilight therefore he began to wield the Keyblade of Twilight once he learned to live with the remaining part of Xehanort that was connected to his heart.
2. Kairi is a Princess of Hearts - who are basically cheaters because they have a bunch of extra rules about their existence and abilities. But everything important is, she became a Chosen One when she came in contact with Aqua (Sora/Ventus - Sky/Wind, Riku/Terra - Earth, Kairi/Aqua - Sea/Water).
3. Roxas is Sora's Nobody which metaphorically makes him Sora himself. Not literally as Nobodies become own individuals but their existence is always a part of the Somebody entity. And thus they share essential aspects of them, physically, spiritually, et cetera.
4. There were many Keyblade Users. Birth by Sleep alone show a bunch of them after the Keyblade War is over already. I do not really want to spoil more though.

So Sora wasn't chosen because he was a worthy guy, he was chosen because someone else's heart is in his? Also, does that mean he has another nobody then? Or is the nobody mixed up with Ven's heart and will never be free? Because obviously for Sora to continue he had to merge back with his nobody. I feel like I've been playing as a false hero this whole time if that's the case.

1. No, Sora very well also is strong. It is not just because of Ventus alone. But it is not like Ventus plays no role at all. In Kingdom Hearts we already learn that every heart has a different kind of strength. Sora's strength comes from his Sailor Moon-like bond of friendship.
2. He has no other Nobody, no.
3. Roxas is both mixed with Sora as well as Ventus. Same goes for Xion who is a clone that was supposed to absorb Sora's existence and replace him. Xigbar even saw Ventus in Xion.
4. Sora was able to continue just because of plot - and Kairi with her superpowers gave him back a body. But as we were able to see, to be fully and completely restored, he had to be reunited with Roxas and Roxas had to accept that before everything was fine. That needed the entire KH2 until it happened. In the end even Roxas realized that the Somebody he was born of was so special because of the friendship he appreciates.

And Kingdom Hearts was never supposed to be standalone. The ending and secret ending show that.