I agree with almost all your takes. The bears and coilers do feel meaningless among the excellent minions Marcus has access to.
I to am a bit confused with the differences of Marcus 1 and 2. I think Marcus 2 is meant to counter intuitively play a slightly slower spread out scheme game. Not having that initial 4 inch group push, spreading your mutations a little slower with than Marcus 1 and having a global mutation applier makes spreading up into 2 or 3 "parties" more appealing than crowding around Marcus 1 for card draw, charges and mutations.
I do think you underestimate the Scorpius. I made the same mistake but the feeding should be looked at as a tech action for poison crews and the rest of the card is independently strong enough.
The main thing the Scorpius is good at is offense, having a stat 7 min 4 damage attack (3 for second attack in turn) is a lot of accuracy and damage output for a 7 point model, especially one with a bonus move action, armor, and a powerful tech action for matchups where it should struggle.
In terms of mutations I tend to lean toward wings because of the creep along synergy helping you land 2 hits for that stat 7 4 poison value. armor 2 is good especially with Myranda's healing, and horns for charge through + onslaught with adaptive evolution is a powerful aggressive play especially with Marcus 2.
