Now it's scientific. Non kosher meat tastes better.
https://m.ynet.co.il/articles/bkkv111rai
This is assuming the same animals are being processed either via kosher slaughter or non kosher processing. This was a case of a group of 20 animals being divided in half, as to control out the variance in input that changes the output results. However, this may not be the case in all areas. It's not economically viable to slaughter unhealthy animals for the kosher market, being as there's a high degree of likelihood that they'll be treif, so it's very possible that the average animal slaughtered for the kosher market is of higher quality than the average animal killed for general market. A study to determine this would need to randomly select beef off the shelf from kosher and non kosher supermarkets and compare them.
(However, it's probably true that while the cheapest chuck or minute steak may be better if you're getting kosher vs non kosher, it's still not a fair comparison given the significant price premium paid for kosher. A fairer contest might be to pay the price of the kosher meat for the equivalent cut in the non kosher market. In that price range, one would be purchasing a premium non kosher choice, and the quality would quite possibly surpass that of the kosher option.)
The article also doesn't go into detail how the non kosher slaughter process was carried out, and whether that mirrors the large scale processes one would expect when it comes to a standard supermarket off the shelf cut. Again, to compare, it may be necessary to test the random supermarket picks for the barometers tested in the article. However, if one had the same budget for kosher and non kosher, it's still likely that they'd end up with a better non kosher product.
In short, while I'm guessing that a $7 kosher burger (or whatever cheapest fast food burger goes for) is higher quality than a $2.49 McDonald's burger, I'm also guessing that a $7 non kosher burger in a restaurant is better than the kosher option. Complete conjecture though.