> Using Latin phrases in law still feels too much like medieval clergy only reading the Bible in Latin and telling the laypeople to trust them.

It's a technical term with a fixed definition. It's not being interpreted, and it doesn't matter if it's English, Latin, or a drawing of a flower.

A lay person being able to guess at the meaning is a minor benefit in some situations, but people guess wrong all the time about how laws work. The end result is a pretty negligible difference.

And looking like normal words without actually being normal words can actually be a detriment to understanding.