... a 40-year-old tax provision that benefits long-time homeowners at the expense of everyone else ...
BS! Proposition 13 prevented counties from taxing older "long-time homeowners" out of their homes. Further, sales of existing homes happen all the time, so Proposition neither hinders "long-time homeowners" from selling their homes nor new buyers from buying older homes. And Proposition 13 does not in any way hinder the construction of new homes. For example, this part of San Jose that was mostly built up in the late 1940s into the 1970s,
https://www.zillow.com/cambrian-park-san-jose-ca/sold/ . Whole lotta sales of existing homes! BTW, while the assessed value of a home is reset when a home is bought, Proposition 13 then starts benefiting that home buyer and does so for as many years as they live in that home. IOW, that benefit is available to anyone, not just those who owned homes in 1978, when Proposition 13 passed.
BTW, I've been a resident of CA continuously since before Proposition 13 passed, some of that time as a renter, and some of that time as a home owner.
If you're really interested in how CA came to have a housing shortage, look to enviro-laws that impede building homes. Look to cities that increased risk with
milk-the-developer fees, restrictions, and take-aways. Look to cities, counties, and the State of California with their rent control and other
screw the landlord laws that make it difficult to earn a living by being a landlord.