Ash's turn

So I was watching the Evil Dead trilogy with a friend of mine a while ago. Sadly my friend isn't as accepting of the quirky strangeness of these films, and she poked a lot of holes in them all, but the biggest one she didn't like was how, between 'Evil Dead II' and 'Army Of Darkness', Ash turns from an innocent, kinda dim reluctant hero, into a wise-cracking smart-ass who cares only about himself.

And after giving it some thought, I came up with what I think is a pretty conclusive answer, although I doubt it's what the film-makers intended.

During 'Evil Dead II', we see Ash turn into Deadite Ash twice, once at the beginning and once at around the end of the third quarter. These scenes both imply that Deadite Ash is still inside him somewhere, but something keeps pulling him back from it. First, it's the sun, but then it's Linda's necklace. The first time the demon was forced away, the second time Ash remembered who he was and fought it off.
But we never truly saw it leave, did we? There was no definite moment where we saw that Ash was alright. Even when he tells Annie 'I'm alright!', she asks him for how much longer, and he doesn't have an answer, which implies the demon is still inside him.
After this, he puts together his chainsaw apparatus, and remarks that having a weapon on his arm is 'groovy'.
After this we see Ash quip and battle his way through several monsters, and by the time he arrives in the past at the beginning of 'Army Of Darkness', he's changed into the badass jerk we all know and love.

But here's where it gets interesting.
In 'Army Of Darkness', we're introduced to the main villain, 'Bad' Ash, who calls the real Ash a goody-little-two-shoes. Ash then blows his face open with the Boomstick, and remarks 'Good, bad... I'm the guy with the gun', as if he himself is even admitting he isn't 100% good, or 100% evil, he's something of a 50/50.
And besides, 'Bad' Ash had to come from somewhere, didn't he? He came from on of the several mini-Ashes which came from the mirror shards, so we can safely assume that they were manifested by the Evil itself... or alternatively, from within Ash, since the Evil couldn't get into the mill, as we saw.
So Bad Ash is pure demon in the form of Ash, the real Ash is about 50% demon, which explains his transition between movies, from hero to antihero.
This also explains how, at the end of 'Army Of Darkness', Ash is almost willing to kill Sheila, even remarking that he doesn't care about her anymore, in the lines:
'You found me beautiful once.'
'Honey, you got REAL ugly.'
It's almost as if, once she became a Deadite, he didn't even care anymore, like he did back in 'The Evil Dead', when all of his friends were converted and he was forced to kill them.

This is why I think that the Deadite version of himself is still rattling around inside his soul somewhere, pushing and nudging him in certain directions to make certain choices, having minute influences on his personality.
So as I said, I think this is the reason behind Ash's change in character between movies, although I doubt this is what the writers intended when they were making the movies.
It's arguably the biggest happy accident in film, completely demolishing all arguments about bad writing. What do you all think?