I have not seen this discussed in awhile and not explain with much visual assistance.
Someone asked, I gave it a quick look, and here's the answer!
"How do I set my Mesa hero to something other than [Druid, Cupid, Santa, Skull Knight, etc]?"
"How do I make PD my Portrait hero so others KNOW I've brought one?"
"Can I manipulate which Hero shows when I'm in Mesa Lobby?"
Hero selection is based on Hero EXP Level before any other factor. If you have PD at a higher level, he will always be the Hero shown to your Mesa team. Evolve stage makes no difference, just the EXP Level.
Level 150 Evo 2 Pumpkin Duke and level 170 non-Evolved Druid: Druid wins.
Beyond Level, the 9 tiles you place heroes on have a priority. If you have two or more heroes of the same level, placing them in an orientation within your team will prioritize which one shows up.
If I place my Druid or Pumpkin Duke on tile 1, that Hero will always be my Portrait, or Avatar, shown to my Mesa partners. With them in that position, I cannot place a higher level hero anywhere else without it being interrupted. This means that I cannot use my Treantaur or Warlock in Mesa or Lava without them showing instead of Pumpkin Duke.
No Talent, Might, MOV spd, ATK spd, Crest, Inscription, Artifact, Hero grade, or other factor makes any difference.
Level first. Position Second.