The West is so big and has so many spitters from nerd/backpack to street style, there is room for both. Iif you look at the history of West Coast rap, it's always accommodates both style. Its just the gang culture in the West didnt make it really viable to have a permanent street league outside of the Bay area.
The incorporation of a street style has always been there, people been talking about killing each other in rap battlers since forever, doesnt matter if its black, white, beige, brown, yellow, green and anything in between. The difference being the over reliance on long multis by the nerds/whites/backpackers and saying shyt just to make the next multi rhyme. While the street battlers, didnt care about how many one word long multi syllables they can fit in, it is about getting to the point as quickly as possible, hence the flow of the street battlers is better than the other styles, you can use Diz as an example. It's just over the last couple of years of the URL talent going over to KOTD, the styles have blended into one another, so its not really a case of us vs them, any more. It's like when the street guys use to clown the nerd/white guys about jokey bars, when jokey bars have become more implemented into the street style as well, but don't be fooled jokey bars in street bars have always been there. And because of the likes of Diz, Hollow, DNA and a couple of others, more street battlers are incorporating freestyle rebuttals into the rounds now.
Thesaurus/Illmac had to evolved because nearly everyone post 2007 and not a street battler copied their style.