Personally, I see nothing wrong with giving Venom non-Spidey origins. By focusing on just Brock & the Symbiote, it adds a bit of depth to both characters, rather than just having Venom being an extra violent clingy Ex, or Brock just being the worst reporter.
That being said, these trailers haven't convinced me that Sony can do a good Marvel film, without Marvel holding their hand.
Still, I hope to be pleasantly surprised. And if it comes out good, than there's a chance it could be incorporated into the Marvel films. I mean, the idea of doing bad guy origin movies has merit, since it can set up a future super hero film, in which you don't have to incorporate the villain's backstory into whatever story you've got planned.
That seems to be what Sony are hopingbfor. They're betting on Venom being a success and thus being the lynchpin for their tiny little piece of Marvel. By throwing up plans for Venom, Black, Silver Sable (possibly?) and Kraven the Hunter, there's been speculation that they could either be trying to build a universe to slot a Spiderman into, should they get sole ownership back. Or, they plan to serve up their group of to Marvel with a 'do you want these in your MCU? Can we have some money?'
This is all just grain of salt speculation of course.