by that definition everything the government ever does is playing favorite, and equal protection before the law becomes meaningless.

No. Equal protection makes sense when you view it in its proper context. The government can't make discriminate against individuals or against race/gender/sex/etc. categories. However, there is nothing in the equal protection claws that say the government can't discriminate with regards to income, home ownership, attainment of degrees, etc.

you certainly can define it in your personal head canon, but to call this definition useless would be an understatement...

I'm not defining it. I'm simply taking it for exactly what the word means. Personally, I want to abandon using the phrase in this context as it is grossly misleading.

that is easily refuted by pointing out that there are tons of laws that apply to companies of different sizes, but if they apply they have to apply to all equally.

If you have different laws for different groups then they aren't equal. There are different rules for Company A versus Company B.

Now the laws are equal within the arbitrarily defined categories set up by the government. But, it is absolutely critical that we understand that the government did in fact create these boundaries, and by definition has to create these boundaries if they want to create legislation.

My point is somewhere down the line the government has to create a boundary on what is and isn't a marriage. Now we can argue where the line is, but it is absolutely absurd to argue that the line should be drawn a point "X" if you use the argument that the government shouldn't have a role in saying what is and isn't a marriage.

all of this is already possible,

I can't marry my uncle.

you don't have to pass a test that you really marring your soul mate before getting married.

Then why have any marriage law to begin with? It seems to me that your actual position is that the government shouldn't have marriage laws, I don't know why you don't just come out and say that.

still totally besides the point.

No, it's the whole freaking point. If you are arguing for the expansion of something, then you have to be able to defend why the expansion should stop at the limit you've perscribed.