Venom is still the Villan in most cannons, but I think the reason he's the hero in his movies is 1. It's his movies, of course he has to be the hero, and 2. He hasn't meet deadpool in his movies.
Iirc Deadpool was actually Venom's first human host.
Deadpool having 3 personalities was too much for Venom which is why he was so fucked up when he latched onto Spiderman. He was literally trying to put his head back together and that's why Peter was able to reject him.
I don't think it was a retcon, so much as an alternate universe. Let's be honest, the continuity of comics, is a fuckin mess.
But yeah, there's a comic where Deadpool is the first human host for Venom and it causes Venom to go crazy, because he can't deal with Deadpool's multiple personalities and overall craziness.
Then he meets Brock, but Brock doesn't bond at first, so venom finds Peter but because he's weakened from Deadpool, Peter was able to fight Venom off.