Is Dark Rebellion Xyz Dragon really as good as people think? Someone said it's good for OTKs but it can't even OTK the opponent on its own because it can only inflict 2.5k damage. Am I missing something?
Yes. You missed this line: "...and if it does, this card gains that lost ATK."
For example, your opponent has a BEW, er.. Dark Magician (2500 ATK). Dark Rebellion Xyz Dragon halves its ATK to 1250, then gain 1250 ATK. In the end, its ATK becomes 2500+1250 =3750.
Imagine if it does to a stronger monster with 3000 ATK like BEW,.. err. Red Dragon Archfiend. In the end, 4000 ATK.
I don't think he missed a line
The monster can't otk except under extremely niche circumstances, and even in the example you gave it still couldn't otk, all it would do is swing for 2500 damage unless you had some way to open his field up for a direct attack that can't be disrupted
Yuto has a Skill that basically recycles 2 Spell/Traps from the GY so you can use Dark Rebellion´s effect again. That´d make the OTK easier to pull off.
Actually, 1 Blue-Eyes is already enough. Use the effect once: Dark Rebellion gets 4k ATK and Blue-Eyes is at 1.5k. Use it again and you'll get 4750 ATK and can attack his 750 ATK Blue-Eyes.
2 materials + a skill that would only work for that + the requirement of the skill (either tossing 2 pk spell/traps to gy fast enough or losing 2 cards in your hand) just for the chance of an attack to otk if it happens to go through?
What that attempt of troll suggests some comments above looks far more reliable