I sense (Sony/Pascal) still have strong desires, to have the Spideyverse they are trying to create, have some symbiotic relation to the MCU. Putting the majority of their efforts & trying to prove their worth, essentially in this one film, to Fiege...with the production staff & casting, wanting to make an impression on inclusion...to whatever degree.
My guess, they're (S/P) leaving the interpretation of the origin opened, to retrofit it's relation to Spidey, should negotiations for renewal goes in their favor. So, I imagine Venom comes into this film already established. They may distribute some convoluted signs of his moment of origin, but difficult to ascertain...to retrofit it later. We shall see.
Still, I sense whatever they do, as far as, the origin is concern...Brock's hatred of Spiderman, will be fueled by his jealousy, rooted in the Symbiote desire to bond with Peter/Spidey over him. His bond with the Symbiote is so intimate, he may feel, like a scorn woman, if he can get rid of Spidey, remove him out the picture, there's nothing left for the Symbiote to desire but himself(Brock)...that's possible his motivated hatred will stem from.