User blog comment:BannedLagiacrus/Monster Appreciation Week: Hellblade Glavenus/@comment-33581177-20170221170226/@comment-20010297-20170223172212

You lvl up deviant quests by finishing deviant quests. And a lvl 1 deviant is definitely weaker than lvl 10, and higher lvls tend to have higher rarity drops for higher upgrades of deviant equipment.