I actually think I do agree that football is the right move for him, in terms of financials, fame, upside, etc. Right now, they're projecting that he'll go in the 1st round, although that certainly could change.
If he goes as low as 32nd, the last pick in the 1st round, that's still a 5M signing bonus with a 10M contract, which is certainly larger than he has with the Athletics. If he goes say 15th, to the Redskins, that's about an 8M signing bonus with a 14M contract.
Additionally, there's far more room for endorsements as a 1st round QB in an NFL market, inherently increasing the value of his worth.
Lastly, that contract would be 4 years in the NFL, with a team option for a 5th year, somewhere around 10-12 million for that time frame. If he's good, guarantee that 5th year and then a massive contract in excess of $100M. If he's horrible, then he's probably done or maybe gets a smaller contract for another couple million in free agency. If he's average and shows that he can play, he's going to get a job and he'll make 5M per year to be a backup QB.
In baseball, he's going to be in the minors for probably 5 years because he has a lot of work to do as a player. He's got a lot of potential but he's extremely raw. Would he make it to the majors? I'd be absolutely shocked if he didn't. Over 80% of 1st round picks do. But it takes a long time to start truly making money in baseball and the odds are just as stacked against you as they are in the football. The difference is that he'd be starting football out on pedestal, has a larger first contract and a quick turnaround to get that second contract.
In reality, neither of these are bad choices but if he'd rather play football, than good for him. Quarterback is one of the least dangerous positions, given the precautions that they take for QBs and the limited head trauma that they receive, so the merits of the discussion of long term brain health don't apply as much as they would in a different position.