Unfortunately the 10th amendment has been undermined by disingenuous readings of the commerce clause and other fuckery, and states and people have whatever scraps of power congress / the feds don't feel like asserting. If you don't like it, well, lol, the civil war established the states cannot check federal power by seceding and as we are witnessing the sky is rapidly becoming the limit.

There's still plenty of difference between e.g. Texas and California.

There ought to be some significant level of cohesion between constituent states in a federation (like the US or India) or even a confederation (like the EU or Switzerland), else the common market and the common law system won't be able to function. It should not be overdone though.