The problem with Zero anchor is that, for the most part, he requires both X-Factor **and **meter to make it happen. In X-Factor 3 you’re free to just press buttons and spam moves and you’ll eventually get a hit, and I’m sure there’s a few X-Factor 3 loops that’ll 100%. However, Sougenmu is extremely vital to anchor Zero. Not just for lighting loops to finish off characters solo, but for safety, and to take the place of Zero’s assist.
Level 1 buster spam during sougenmu is a great way to hitconfirm from pretty much anywhere, since they’ll keep comboing long enough to run up, shoot again, run up, shoot, etc etc. until you hit them with a launcher. It’s also a great thing to activate when you absolutely need to stay in, because Sougenmu activation nullifies advancing guard. Since you won’t have assists it’ll be hard to set up unblockables, but you’ll at least be 200% safe all the time. As long as you have Sougenmu you’re opponent won’t be hitting you.
As for team composition, the only reason to have Zero in the back is if you put him there to regain health after fighting on point. Anchor Zero might be good, but I don’t think it’s the best use for Zero at the moment.
But now that I think about it more, I want to give anchor Zero a chance, because I think there’s a lot he can do that no one’s really tried. For example, after fighting with Zero on point, activate Sougenmu and put him in the back. An incoming Sougenmu’d Zero has an easier time of getting out of incoming setups than without the shadow. Not to mention all his great assists. You’ll also have access to the invincible crossover counter 100% combo if he’s in the back, but he can’t have Sougenmu on.
Either way, I wouldn’t put Zero in the back because he’s too good at using assists, and only a few other characters can use his assists in meaningful ways (Dante, Vergil, Sentinel, unless you count anyone that could use a 100% crossover counter, like Chris or Strange)
But if your team order gets messed up in a fight and it’s all up to Zero, I would still say he has a chance if he has the resources he needs. Now that X-Factor is buffed from vanilla he just might be a threat as an anchor.