I think SRAM dicked with the naming structure for 1x11. My X01 or whatever it is rear derailure is not as high end as my X9, it's way heavier and way more metal/cheap. It's whatever one is one step down from the best right now in sram 1x11.
THOUGH
The X-Horizon rear derailure is by design heavier, it's a really nice upgrade. It's a nicer design to keep the chain taught on rough terrain.
I still have 9 speed on my hardtail and my fatbike. Not because I'm stubborn but because it hasn't broken yet. My hardtail wheels aren't hardtail compatible so I'll likely never go 1x11
Also my SS wheel is 135mm ONLY, so I'm probably going ot be stuck with 135mm rear ends for a long time since I really like that wheel.