As an SF cyclist, that's not entirely true. Most commutes in the city end up in SOMA, the Financial District, or the Mission, and require little if any climbing. On the way home, even going to areas like the Haight have paths such as the Wiggle that aren't particularly steep and can be done sweat-free.

Obviously some people live and work in areas where a sweaty climb is unavoidable, but far fewer than you seem to imply. And it helps a lot that it's virtually never hot here.

Having moved from Georgia, it doesn't matter if the route is flat when it's 95 and nearly 100% humidity. That's way more relevant to sweat than the SF hills are.

The human body adjusts to a remarkable degree. The first days or maybe weeks of a new bike commute can be a sweaty experience but it ceases to be a problem quite quickly. If you were in the gym, that would be your cue to increase workout intensity, but since it's a bike commute, there's no need.

For a grade over a certain percentage and longer than some duration, it is probably indeed the case that sweating is unavoidable. But you can usually trade a short steep grade for a longer shallower grade, even in San Francisco. The absolute worst portions of SF hills are usually only a block or two long and are much more likely to be found where you live, not where you work.

get an electric bike

Yep, you read that right here under "Cycling to work can cut cancer and heart disease".

as a support for hills, not use it exclusively.

Totally. I commute (and locomote in general) via an electric bike here in Tokyo, where such bikes are very common.

You can get just as hard of a workout as with a manual bicycle — it's just that you go faster and cover more distance.

However, it also gives you the option to pedal lightly and rely on the motor more, when getting sweaty isn't convenient.