I have a default criteria for this market which is subject to change based on two types of market comments, whichever comes first.

TYPE 1: 'Lock it in': A comment on this market that is along the lines of "yeah this makes sense". If this type of comment comes first, the criteria is locked in.
TYPE 2. 'Better idea': A comment that I conclude proposes a better criteria for assessing how seriously each league is taking this (and it doesn't requrie significantly more effort to assess). If this comment comes before a "lock it in" comment, I reserve the right to override the default criteria and adopt that idea as the official criteria.

For now, here's the default criteria:

I will randomly select three MLS teams and three Liga MX teams. I will then compare the starting lineup of their first Leagues Cup group match against their most recent starting lineup in their domestic league.

Resolves YES if the three MLS teams have a higher average similarity between their league lineup and their tournament lineup. Resolves NO if Liga MX has greater similarity. Resolves 50% in the unlikely event of a tie.

Update:
Teams selected
MLS

• FC Cincinnati: 54.5%

• LA Galaxy: 54.5%

• Atlanta United: 63.6%

• Average: 54.2%

Liga MX

• Mazatlan: 54.5%

• Santos Laguna: 90.9%

• Atletico San Luis: 81.8%

• Average: 75.7%

  conclusion: Across 3 randomly selected clubs, Liga MX Leagues Cup lineups had significantly more overlap with their most recent league match as compared with three randomly selected MLS clubs.
  
  Does this suggest that Liga MX is taking Leagues Cup more seriously than MLS? Perhaps not necessarily, but the criteria has been calculated. I would be interested in how different this would be across all squads, but since I might be the only one, we'll leave it at that.