i think it makes sense to play Wildermyth's main campaigns at Adventurer difficulty, or some mix of storyteller/adventurer (or the tried and true "both on storyteller and kick one of campaign or combat up one notch each chapter".) but i have for you a great way to play legacy procedurally-generated campaigns to just noodle around fleshing out your characters or getting a side story with someone who joined in act V of your last scripted campaign:
play on storyteller combat difficulty, with the max 100 calamities to start. it makes the tactics of combat interesting but always-solveable combat puzzles that give you a chance to exploit or show off your builds or combinations, without being so hard that you're ever tempted to reload. this is perfect if you are multitasking, podcast-gaming, or two-monitoring. you will see enemy types you've never seen before in the games. if you need additional difficulty, give yourself some number of maximum turns to try and beat each combat in (frequently 3, and then the big end-of-chapter missions give yourself 6).