Two weeks ago the three star headhunter monsters were dealing out 1000+ hitpoint per hit. After the update they are doing under 100. I finished the 3 star list with no one but Tlanac and Kassia in my party and it was BORING!!! The only challenge was the spider which did some heavy damage but with creative strategy I finished that one the second try.
The real problem here is that things are either too easy or too hard. I write software for a living. I don't know your code but I can guess at some of the challenges you face with the headhunter/weekly missions because you have to scale difficulty based on the skill of the played party. Perhaps the problem here is that you seem to base this off of party level. Yes, the fighting party strength does correlate with the party level but party level grows a lot because of people who are excluded from the fight. We only use four heroes but can have another ten bumping up the strength of the party. I suggest you scale difficulty only by the strength of the top four heroes. Also, please factor in more than attach totals and hit-point totals in the monster strength metric. When attacks per second are down to one or two and damage per attach is more than the tank's total HP the fight gets really hard. When a party faces two, or even three such foes at once things get impossible.
Once you get the headhunter/weekly missions under control go back and look at how you rate the other fights. The general rule is that the loot we get for a hard fight is worthless by the time we are strong enough to win the fight. Why?? because we have gone to higher levels and finished higher rated fights and have gotten stronger in part from the gear we already won. Is this what you intend? Why not have the 3 and 4 star boss and darkness fights give out loot that's not only higher in color but higher in numeric tier? By the time we're beating those levels we have likely unlocked not only the next loot tier but the one after that as well.
Once you're done balancing out the ratings please look at the money and experience awards for the various fights. Pay particular attention to the new portal missions. A replay of Rise of the Demon is rated at 94 but only pays 160 coin. A replay of Unanswered Questions is rated 97 but pays 725!?!
This isn't the only thing out of balance. When you opened up southern Lerona It would take four or five new quests to have my four heros ready to level up. However, I'd only have money for one of the four because the coin earned is not balanced with the coin needed to level. I can see that you might assume that one or even two of the party will have to level up with coin earned by repeat play but THREE?? Take a look at the paltry amounts won in repeat play and calculate just how many many many repeats are needed to pay the 10K, 15K, 19K needed to level someone. Now think about the fact that a repeat fight is not as fun as winning a star. The experience ranges somewhere between "that one is still a challenge" to the more common "surely another game would be better". Finally, think about what sort of experience you want players to have in your game. If you want to kill us with grind and boring fights you're doing very well indeed.
Seriously, I'd like to actually finish this game but I'm about ready to just find something else to spend time and money on.