The SF area already has rail corridors that ran from all major cities (San Francisco, Oakland, San Jose, Silicon Valley, Santa Cruz, etc) to Los Angeles. Most of that project is over farm land, where right of way / imminent domain should be straightforward.

Instead, we get the redundant Bart to San Jose (Amtrak has been continuously providing that route for a century or something.), and SF to SFO (caltrain covers that already).

They need to pick one rail technology and move the entire region to it, then dictate the legacy systems operate in a unified way (allowing regional, independent rail authorities to completely override city councils, sacramento and DC), with the understanding that they will be fired if the transition to a unified system takes more than 5-10 years.

Instead, they are doing the exact opposite of everything I just recommended, and all the systems are falling into disrepair.

the technology is irrelevant, it's purely mismanagement and lack of coordination amongst agencies. modern main line EMUs are perfectly capable of matching BARTs performance.

there are many, many problems with BART's SFO extension (courtesy of quentin kopp), redundancy is not one of them. there was no BART to caltrain connection prior to the SFO extension, and caltrain is a completely unserious transit agency running hour headways.

genuine problems with the transit system in the bay area abound, you should pick one of those to complain about instead of some weird fixation on incompatible gauges

Bart to SFO provided a valuable connection from Western SF/Daly City to Caltrain/SFO. It also provides the actual only connection between Caltrain and BART, giving better connectivity to the East Bay.

Yes, but replace either BART or Caltrain with the other one, and the system would be strictly better than it is today.

For one thing, it would cut 15-30 minutes of travel time between Silicon Valley and SFO, and Silicon Valley and Oakland.