With the help of @egervari, I think we have figured out how to maximize one’s score in Mjolnir Strike, given what one has.
There are four columns in your defense team. For each column, only the higher BST/merge/Dragonflower/SP unit counts for your score. So, feel free to use a suitable unit with a suitable skill set as your non-scoring unit since s/he won’t lower your score.
Depending on the season, mythic heroes score differently. Currently we have the Light seaon as the main bonus and dark season as minor bonus. So, your optimal scorer should be Eir or Peony (assuming they have high merges; otherwise, it is still better to use another unit at +10).
If you do use a light mythic, say Peony. Her merge count is automatically +10. So, if you have a +10 Peony, she’s counted as +20. This is how my Peony can score even higher than my max H!Hector.
Finally, since placing in different columns give different types of bonuses (spd, def, res, respectively) AND considering the need to score optimally, you might need to put some thought into your team formation.
Hope this helps.
This is what I have for now. Peony doesn’t have Aether yet. But 762 could be the current max score possible, if it follows the system of Arena and AA.