Ohtani's upside for the SF Giants is still unparalleled
While a more bearish look at Ohtani's future still shows a guy that should be a fantastic hitter going forward, it is impossible to ignore the potential upside with Shohei if he is able to pitch well again. Before his injury, this was a guy that was set to sign the biggest contract in MLB history thanks to his production on both sides of the ball.
A record deal is probably off the table now (more on that in a bit), but that two-way upside is still possible. Multiple pitchers have now come back from two Tommy John surgeries successfully with Nathan Eovaldi being a notable one and that doesn't even account for guys like Jacob deGrom and Walker Buehler who are rehabbing from #2 as we speak. It is far from a certainty that Shohei will be a dominant starter again, but neither is he doomed to failure.
Let's assume for the moment that Ohtani does indeed need a second Tommy John surgery and for whatever reason, he is no longer able to be a starter. There is nothing that would keep the Giants from trying Ohtani out in the bullpen. While not an ideal situation, it would also be hard to not be excited about the prospect of Ohtani's stuff playing up in shorter relief stints.
In short, there is a case to be made that for the right price, signing Ohtani strictly as a bat still makes sense for the Giants. However, there are a lot of people that are assuming Shohei's pitching career is over and that seems like a mistake especially when calculating his potential value going forward.