Historically coat of plates/brigandine was worn over mail which was worn over a gambeson. So its heavy yes but but not so heavy as to be impossible or even that much of a problem (we are talking professional fighting men after all) its just the trade you pay for superior protection.
Scale was typical worn over just a gambeson rather than mail and lamellar was somtimes worn over mail and sometimes just a gambeson. Of course nether of these were especialy popular in western Europe at the time period Battle Brothers takes as inspiration. In the west scale was a rare armour and lamellar was pretty much unknown other than to the Norse (who typical used coir boli (hardened leather) rather than metal and wore it over mail if the person could afford so.