The difference, by the numbers
They have no ingredient in common: the Oaxaca Old Fashioned has tequila, mezcal, agave syrup and Angostura bitters, the Sazerac Cognac, absinthe, sugar and Peychaud’s bitters. In parts, an Oaxaca Old Fashioned is 3 tequila, 1 mezcal and ¼ agave; a Sazerac is 8 brandy and 1 sugar. By volume, the Oaxaca Old Fashioned is 92% spirit and 8% syrup and sugar; the Sazerac is 87% spirit and 11% syrup and sugar. Different bottles, similar balance: that makes them close cousins on the ratio map.
The Sazerac is the stronger drink in the glass (25.2% ABV against 24.7%), but the Oaxaca Old Fashioned is the bigger drink, so it holds more alcohol (1.41 standard drinks against 1.19). The Oaxaca Old Fashioned has more calories (about 159 against 132), with about the same sugar (4.6 g and 4.0 g). Both are stirred and served in a rocks glass.