Lol.
Duopoly : If you want to watch football in Scotland you have to pay through the nose because you can only watch Rangers and Celtic. No other teams are available.
Not a duopoly: Celtic and Rangers win the league but you can watch who you want.
Not really sure what point you're making about walmart and sainsbury but there are specific exemptions from competition law for sporting competitions. If there weren't, the SFA, SPFL, LTA, BAGA, the lot of them would be classed as anti competitive cartels.
While part of me is just being pedantic because i enjoy it, i also think it's important to understand what the problem is. The problem is a failure of collective action on the part of the clubs. There are, what 40?,clubs in the Spfl that aren't the cheeks and if they could act in concert to distribute money and make rules more fairly then others might have a chance.
Or you can go full Scottish Football Monitor and write to the EU and the mergers commission.