Since it's a fighting game, he's playable and hella fun (big, meaty, plus on block normals). Yet I am quite glad that he never once sat in the main antagonist seat. Terumi, Nine, Izanami et al. were far more suited to the task, even in the trainwreck that is Blazblue's story.
This is about as helpful as me counter-claiming that characters such as Balrog in Street Fighter (despite being a no-story train-wreck itself) can be endearing to some people even though his entire story is "Imma punch you really hard for mah fight money coz I'm totally not a Mike Tyson inspired character". You don't have to be complex and/or capable of sitting in the driver seat to appeal, which leads into...

It's possible to like Zenos and antagonists like him, while still admitting that they aren't suited to run the show.
Entirely assumption, for now. I doubt he will be the main villain. If you ask me, it'll be more about characters in the background capitalizing on the results of Zenos' bonkers antics, starting with Garlemald in utter chaos, with Mr.WhiteRobe on his little moon-office twirling his moustache as things get crazier. Plenty of room for other characters to be introduced and shine as well now that the Ascians are almost extinct and prominent Empire characters are either gone or in trouble.

I have already made numerous comparisons between Grynwhat and Zenos. Grynwaht is that Garlean antagonist that is alike to Zenos
Which was already debunked. They are nothing alike whatsoever.

I would say it's inspiring that people would want better written villians in their video games.
Do not mistake my critique of the reasoning people use as some sort of affront against better-written villains. I've liked the humble majority of villains in FFXIV, actually. Even if you restrict it to the empire alone - Gaius, Varis, Nero, Darnus, Regula, heck, even schmaltzy characters like Livia could resonate with people on some level. Then there's Zenos, who is refreshingly different from every single one of them by a country mile.

Just because the antagonist's game function is little more then bullet sponges doesn't mean they should have to have the motivations of a sponge.
And we're back to this apparent need for a character to have fleshed motivations or goals. We've had plenty of those and will continue to get them on tap for as long as the game goes on. I'm quite welcoming of the occasional character who goes against the norm rather than follows the same old assessments. There is no shortage of complex characters. We've had a fair share of twisty-turning villains, or others that are straightforward but work through (or are defined by) complex background shenanigans. Zenos is the first (main) villain to bypass all that at the expense of everyone around him, even his own so-called allies. Practically the entire roster of empire-related villains have oft been hyper-patriotic and either borderline racist or (insert Garlemald v Eorzea thought-train here that conveniently allows us to quickly build a natural dislike for them as the 'baddie faction'), usually with a slice of Ascian influence on the side. Zenos doesn't apply there either, because he's confined to his own bubble and couldn't give a damn for their way of thinking. For a game so centric on Light vs Dark 80% of the time, I'm more than happy to have at least one villain who could make things go either way out of sheer apathetic arrogance rather than yet another hair-brained scheme backed by some obnoxious monologue about how powerful X is or how unstoppable Y is until they're laying broken at your feet and everyone goes home for tea. Again.

Having said that, I'll repeat my earlier comment - I doubt Zenos will be the front-runner. He'll be the seed sower and the thorn in the side, but bigger fish to fry will loom above it. As much as I like Zenos, there's no reason to believe they'd go from someone like Emet to Zenos, but they most definitely can utilize him much the same way as they did Vauthry as the door-man under the guise of being a big player.