Are you certain you want Wall tribal effects? The Walls of the times of Legends are nowadays mechanically any creatures with defender.
I feel like RotE did the "defender matters" thing. I like the Wall flavor.
Plus, I feel like there's more room for shenanigans with Wall than with defender. I mean, Mothdust Changeling + Calamity Glyph is a new Glistener Elf + Might of Old Krosa (let's just be upfront about that combo in the evaluation here... not to say that Mothdust Changeling itself would be in L2.)
Also, as for another topic, I mulled the idea of creating black and green entries into the cycle but I decided that "Wall matters" would be a subtheme best left to a narrower color pair or trio. Plus I couldn't come up with good ideas for the black or green ones, anyway.
Wall is a good creature type. I don't think it should be the only creature type to get defender, as it was in the early days of Magic, but it's definitely legit. I like the 3 in the OP, and agree it makes sense without being a full cycle. Green and black really aren't big Wall colours imo. White and red seem like the main ones.