For Berkeley specifically, it is easier to be admitted to L&S (note: all L&S frosh enter undeclared) than most or all CoE majors. However, changing into a CoE major from a non-CoE division is very difficult. In contrast, getting admitted to a CoE major is likely more difficult, but changing into L&S later is much less difficult.
Also, from a curriculum standpoint, it is not required to major in biology to do pre-med. Some engineering students do add the additional pre-med courses, though the schedule can be very crowded. Bioengineering is popular among frosh applicants (and therefore one of the most selective for frosh applicants) probably for this reason, since it includes most of the pre-med courses already.