Well, obviously you'll never have a trial of a single infantry, no matter what armaments he has, in one-on-one fight. It wouldn't even be funny, and dishonored both participants.
There are plenty of examples un-augmented trials between Mech-jockeys and Elementals, it's practically the SOP in a trial between them. It could be augmented with swords and pistols, but not power armor. Remember that even though elementals are bulkier and more muscular, the Mech-jock has superior speed and reflexes, so they're practically on even grounds; also, elemental are trained to operate as team, while pilots are encouraged towards personal excellence.