N=1 anecdote: good friend’s son is a jr at Cal and is bio/premed with a 3.9. He is also on 2 club sport teams and seems to party a lot. So it can be done, but probably harder at Cal than most places.
The disturbing thing about UCLA, Cal, and UCSD (especially)is how low their med school admit rates are given the caliber of students admitted there as Freshman. Put a kid admitted to Cal in a small LAC and they will likely graduate with a GPA . 5 higher than had they gone to Cal. This GPA boost has a huge effect on admission chances to med school, as does better letters of recommendation and superior counseling (non-existent at most UCs).
Your right about comparing acceptance rates. However the UCs don’t game their numbers so you can def. say Cal, UCLA, UCSB >>UCSD,UCD>>UCI.
Private schools often use premed committee letters to filter out/discourage marginal candidates from applying. So take their numbers with a grain of salt, but I know for a fact the likes of Pomona and Amherst have really high admit rates.
Good luck!