Featwise of course he's obviously a monster. But there's also hype.

-chosen by Netero.

-Knuckle's comment about his aura pool.

-Cheetu thinking of Zeno as a warm-up for Morel. Cheetu's a dumbass tho.

-Killua calling him very strong.

-Pitou, Youpi and Pouf all praised him. The three that got Pitou excited were Kite, Morel and Zeno. That's the league he's in.

-Considered for triple star, which while stars don't always translate to strength, does say something.

-Chapter 199 seems to hint that he's a nen master due to him lecturing Killua about being one, which seems to be the case, as he uses manipulation(controlling the clones), emission(seperating 216 troopers from his body), enhancement(buffing up before Gon and being physically tough in general), transmutation(being able to shape his smoke quickly into troupers or other stuff) and maybe conjuration(color on the clones).

I'm Morel fanboy number 1 tho, i'd rate him above Zeno, so i'm biased as fuck. Tho i find it hard to not be a fanboy, if you take a glance at his feats it becomes clear he's broken as fuck, even among the hxh high tier.