Yes, but in practice as a transit user (not in the bay area), rail generally ends up being more practical. Typically trains come every 3 to 10 minutes. In theory, buses could be this common, but more typically they run every 30 minutes or so. And taking into account a typical trip involves a transfer or two, this can make even short commutes over an hour, not acceptable to most people. The goal of transit isn't just to provide an option to the destitute (although it is nice if it does), but to make a serious impact on congestion by making a better alternative to driving for people who otherwise would have done that.
Frequency of service is entirely orthogonal to the type of service.
London has a bus route that runs one bus per minute in peak times. Because London's streets are busy this means you will usually be able to see _several_ of the buses on that route on a street you're on that's served by that bus, and choose whether you'd prefer to walk to the closest stop, or walk in the direction of your bus and catch an "earlier" bus that is further in that direction already.
One per minute is actually a _higher_ rate than is achievable by London's automated and semi-automated underground railways, none of which even aim for more than 38 trains per hour in peak.
Now, of course S-series underground trains carry about a thousand people, whereas a London double decker bus maybe carries 150 (both would be crammed in this scenario but that's not an infrequent occurrence for peak hours), so the trains on a core route are moving about 35-40 thousand people per hour while these buses move less than 10 thousand, but for you as an individual the buses are more frequent, not to mention they're right there in the street, not at the bottom of a shaft somewhere.
