Variants can still be for progressing players. Those progressing players being the thronebreaker players. You could shift to 5* 3-4 gems for completion per chapter (why waste the t2a), a 2-3 for completion, and 1-2 class based for 1-2. All 6*.Add in some sig stones, maybe 2 6 stars (or 2,5). And for exploration add 50% of both t6b and t3a. Difficulty equal to 7.4 with maybe somewhat higher attack values as variants typically have those compared to their respective progression.