There’s zero national economic gain from _any_ variation in law from state to state, but either you’re in favour of state’s rights or you’re not.
Yes there is. States compete with each other and this prevents any one of them from having laws that are much crappier and more oppressive than average because when that happens businesses and people leave.
Not as unusual as you would think, given that it is a basic principle of both the EU (despite what Eurosceptics would have you think) and the US.
There’s a case to be made for variation, but that ain’t it.
Its not surprising that one US right wing think tank thought the UK with its "socialist" NHS and higher income tax was a freer place to business.