That was fast. Unless this tax targets all of the bay area, the moving cost is not really much and your workers could still commute with a WFH option. Imo, San Jose is in prime position to build a real city with the possible exodus from SF.
Population essentially doesn't matter - people are talking about density here. For example, Phoenix is essentially an enormous suburb with giant malls, and you never hear of despite its population numbers. Boston is a small city with rich urban life that occupies an outsize role in the American psyche.
SJ is big by population but it's essentially a tiny downtown and a huge spread of suburban single-family homes and strip malls. And (before the covid mess) the traffic was already not great. So if we ever get back to in-person office working, and after Google sets up their new office in SJ and others will consider doing the same it probably is going to suck big time. But if it will be "mostly remote" setup then SJ has plenty of space and opportunity to accommodate more business.