This is my city, and I don't know anything about this dude pre arrest, and don't follow basketball or colleges, but here's a rundown:
The area where this happened is extremely rural and isolated, this would be Jamul.
The area where they are prosecuting him is El Cajon, kind of a B venue, as opposed to Superior Court in downtown San Diego, regardless the prosecutors are often extremely good, and gunning to get moved up, and are extremely experienced with gang cases, as El Cajon has many of them.
The Sherriff's Department are not A1 investigators. But, that is their jurisdiction as it happened in the unincorporated county.
The evidence against him is extremely solid. They have bullets in the car, witnesses, geo location/phone data that puts the cars and people in the scene of the crime at the right time. They have witnesses who are cooperating. probably not that smart, but whatever. This isn't rape, where it's he said she said, you have multiple witnesses and bullet holes, plus shell casings. What they probably have too is texts sent in real time confirming it. They don't need to give up everything at the prelim, just the basics.
What they don't have and probably needed was JJ Taylor's cooperation. Because either he or Mikey pulled the trigger. I don't know these guys, but I know whats up, they are little kids with wild egos and money up, rent (*buy) a home way out there to try and duck all the problems someone like Williams could get into in either downtown or whatever. They are also probably wannabe gangsters. Don't understand the consequences of their actions, that they could have easily killed or shot someone in the car. It's just luck they didn't.
As for taking it to trial, or plea deal.....he's going with a bad attorney for one. It will depend on variables that are unknowable to me, but seeing the evidence, just at the prelim, they can win at trial. The guys wearing a bow tie. he needs someone better in there. I would guess any plea deal is going to come with custody and felony conviction, and that derails his career, which I think is over anyway it lands. He misses just a year or 3, and he's done, right? No chance for the pros, and no chance for college.