> It is perfectly legitimate for a company to be incorporated in Delaware and to register as a foreign corporation in other states where it has a presence/does business. You can pick any random Fortune 500 company and look up its registrations in the states where it does business.
It may be legal, but it's rather more questionable if it's legitimate: the latter is a value statement in casual language, even if legal jargon would be more precise.
If I do business with people in all states of the USA*, there should not be any particular state which attracts a majority of big (and everything bigger than "small") business registrations: other than network effects (e.g. everyone else does it so the corporate lawyers are all right there), anything pushing so many businesses to choose one specific state, be that for taxation or for a court system that presumes more in favour of businesses than elsewhere, this creates an uneven playing field for other states and who gets what powers of enforcement for business (/consumer) laws they pass.
Like, people here argue the EU is "anti-business": well, the American-registered factories (Tesla) and American-owned IT company offices (Apple, Microsoft, Google, etc.) are still here, and the shares are publicly traded so even us Europeans can own them, but they count as "American" because of where they (/their parent companies) are registered. Even Google Deep Mind (HQ: London) gets called "American" due to the ownership structure.
* A similar argument applies to the EU