Of course you are correct on both points. But subjective doesn't mean "wrong" or "open to every interpretation", it just mean more than one interpretation, and often narrowing down possibilities makes the truth easy to see.
Different people disagree for different reasons. But only the most deranged disagree that what they can do and effect is worse evidence than some authority. So things like "trying it for yourself" have worked consistently as evidence for most of history. Today "it" can be a bunch of different categories of experiments and experiences.
Even then lots of experiments are out of reach of most people, sometimes financially, sometimes intellectually. Some people think essential oils helped their cold go away in 3~5 days when most colds go away on their own in 3~5 days and. So there needs to be some delegation of authority. This is where a lot of problems leak it. Some people grant authority to some for silly reasons (like an a priori assumption they can do no wrong) other for good reasons (like lots of experience working in a relevant field with many published papers).
For many people exploring the different levels of subjective evidence can get two people to understand why the other believes something goofy. This takes time, isn't guaranteed, but it can be done at least some of the time to show where evidence and many beliefs fall on a gradient of quality. This fails when people hold some belief as firmer than reality, like what conspiracy theorists or religious zealots do.