Not necessarily a problem. Only 2 consistent winners? If this was implemented, someone running a unique defense team that won 1 in 10 times would get more matches and more wins overall than someone who ran meta. You can see a minor version of this already in place- you get noticeably more defense battles running 4x Firebomb than meta right now.
As far as impacting people’s ability to repeatedly farm the easy or stalling teams, that’s not really an issue either. You’ll still see those teams when people set them. We aren’t meant to have readily available access to insta-lose defenses- that’s why 1 troop defenses were removed so long ago.