with the spell, you create an magical wall composed of energy that sort of replicates the effect of prismatic spray whenever you enter it, prismatic spray also being an evocation spell. Every other spell in the "wall of x" format are evocation spells also, even wall of stone, wall of thorns etc, all things you would normally expect from maybe the school of conjuration.

and yet despite all this, the spell prismatic wall is an abjuration spell? yeah i get that yeeting out an spell that completely blocks spells, ranged attacks and movement would fit within the abjuration theme of "negation", but every other every similar spell seems to be an evocation spell. Is this possibly some kind of oversight/ typo or is this some kind of holdover from a previous edition or is this an intentional part of the design? is this spell just considered so protective by its features that it fits more closely with abjuration than evocation?

Abjuration is for any spell that is more designed to protect you. It doesn't matter if you summon (normally conjuration) or manipulate/create energy (evocation) or whatever, if the primary intent of the spell is protective then it goes into Abjuration. Abjuration is a trick school. Other schools are named by the type of magic, abjuration isn't it's named by the main intended effect.

Prismatic Wall is designed to protect you. Other Wall spells have uses for utility as well as for offense (especially the Fire one). The Prismatic one however, is of limited use. Other walls can achieve effects if you place it in other creatures' spaces - usually dealing damage, or have strong utility aspects like Wall of Stone. Or can be combo'd with other spells. Prismatic Wall, can't be used for utility and if you place it in another creature's space it fails and you can't really combo it. The wall is designed to provide 7 layers of protection and it's difficult to use it for anything else. That's why it's abjuration.