Type:Null as a tank?

[Wi-Vi]

Move this to gen VII theorymon if you think it belongs there but now that the games have been out for a couple days I'mma create myself a thread.
Type:Null is certainly interesting, he has decent stats all round, the ability to prevent crits, and only 1 weakness.
I noticed Type:Null's stats stay almost the same when he evolves so why even evolve? What do you think of this:

Type:Null
Ability: Battle Armor
Item: Eviolite
EVs: 252 HP, 252 Def, 4 spDef
Nature: Impish
Moves:
-Metal sound
-Tri-attack
-Rest //only recovery move it can learn :-(
-Sleep talk //So that rest doesn't mess you up
//Other options
-Swagger
-Toxic
-Thunder wave
-U-turn
-Return/Frustration
-Aerial Ace
-Razor wind

Type:Null has decent stats all around, but a lackluster movepool, the only stat that increases upon evolving is his speed. Instead of evolving though I'd like to know how he would do with an eviolite status-tank sort of build.
This build is intended doubles where a second pokemon will be able to take a more offensive role. It's still a good idea to have at least 1 attack because of taunt.

 

[Gengarzilla]

Ehh... I'm sure that Porygon2 would do this strictly better thanks to it getting similar defensive stats and Recover, in addition to Trace copying an ability like Water Absorb or Flash Fire. I don't know if they can be found in Alola but that's what I'd recommend if they are.

I noticed Type:Null's stats stay almost the same when he evolves so why even evolve?

For Silvally's RKS System, an ability that changes its type when holding one of 17 "Memories.

 

[Wi-Vi]

I did get the idea from the porygon2 build.
Now that the game is available we know that porygon can be found in Alola.

I might have been been overselling it a bit with "Why even evolve?" but I've tried it out and it's not half bad. (but it's certainly not OP)
I'm not a huge fan of the evolutionary line but if you get one with a bad nature or you want to use him in ru or nu or wherever he ends up here's a way he can be used.