From what I can see I don’t believe Chamber is a Radiant, it seems like his “tech” comes from Astra’s powers, he’s always interested in Astra, especially her arm. Maybe his tech/“powers” come from stealing Astra’s stuff.

People say it’s possible to attain a high rank and climb, but i’ve never seen a Radiant level player that has started from the bottom. They’re always at least immortal skill level wise when they started playing valorant.