He has
Purgatory Onigiri is the time skip variant of Onigiri
Theoretically it should be stronger than the Flying dragon slash
So Zoro is using a weaker technique than the one he used last chapter
The reason is obvious. He’s realized physical attacks don’t work so he pulled out a burning attack, the one with blue flames that obliterated Ryuma. It’s a weaker slash but it comes with burning effect.
It’s kind of interesting. Zoro is actually using tactics here. But of course we know, if he keeps holding back on that armament haki, he won’t get anywhere