I know I will never change your mind, but...

1950s/60s are way over and done with. At the time, cars ruled and buses were what remained of transit for those dependent on it. The rail systems were worn out and bankrupt, and even when a government agency (like LAMTA v1.0) got one there was no funding or desire to resurrect what little operating rail they got. There was no federal support for transit at the time; it all had to come from local taxes and fares so the cheapest mode (buses) won. Face it: with only a few exceptions, rail transit was dead by the 1950s. It was reborn in different formats at various times in various places over the next 30-40 years.

By the 1960s, we had cars that could cruise at 65-70 mph (my family's '63 VW had a top speed of 72mph and could maintain that indefinitely on level ground) on point-point (no passenger stops, no transfers) trips, with good a/c in American cars if you had the money for the option. Nobody who didn't absolutely have to would ride a 50-year-old PE car rattling and bouncing along at a top speed of 35-40 mph (average trip speeds usually around 10 mph). Museums and short tourist rides are about the only place for that, now or then. Comfort and speed expectations had changed by the 1960s, and BART was the first system to directly try to meet them.

BART was designed as it is for reasons that made engineering and management sense at the time. The fact that it wasn't maintained well for a long time (in favor of NEW SHINY extensions) is a management failing that has been partially corrected. But at nearly 50 years old, BART's about the age of PE in the 1950s, and a lot of significant things need to be fixed if they're going to keep running and even come close to meeting demand. Nobody will cough up the HSR-competitive billion$ needed to truly start over, so fix what's there and move on. Again; objective reality vs. alternative reality: it's there, and the most cost-effective option is to fix rather than replace. And BART's not the only place: Amtrak has the same problem.

As far as I can tell, there are no unbreakable commitments yet for HSR alignments between Bakersfield and LA. Measure M afaik doesn't have any significant HSR components - LA has enough to work on otherwise. There's a strong preference in many quarters for going via Palmdale, and there are good reasons for it. But nobody has spent money on any more than studies so far south of Bakersfield, and funding just doesn't exist to do any more than that yet. So if you and your friends feel really strongly about Tejon Tunnels, and can build a good objective engineering and business case for them as opposed to going through Palmdale, here's your chance to make a difference! You'll need to engage in good old fashioned politics. Complaining about things here does nothing; building a good case with the politicians and technical agencies might. Go for it, and if you're successful then just maybe you'll be a factor in avoiding the next BART. FWIW, I'm on the fence regarding routing via Tejon rather than Palmdale, though probably not for your reasons; of course, I don't expect to live long enough to even see construction start over (or through) those mountains, let alone ride the train.

Happy Election Day Eve!