I think there is something mixing from your explanation. You used only fiat to do a calculation and I wonder if the same 15% tax is applicable when you want to calculate the gross gaming revenue in bitcoin.
Let says for example A casino A has a total number of 100 BTC as GGR, is the company going to pay the same 15% for tas you specify on share stake? You know there is a specified percentage of Tax a liquid crypto earner is supposed to pay to internal revenue service.
I'm interested in how companies that accept crypto deposits pay their tax, maybe it's the same way they do with fiat they do to cryptocurrency, I couldn't find tax on casino in most of the crypto tax books I have seen.
I still think your examples were not well simplified as they should be.
NGR is the only way to determine how much the Casino will pay in Tax. Companies that accept bitcoin paying taxes in bitcoin is not logical because they still have to change to fiat so that they'll be able to pay their tax unless they are in a state where people can pay their tax through Bitcoin. Provided that the tax percentage is specified then NGR is the formula to solve and get the result.