Thats quite a straw man. There's a pretty big difference between using a benefit as intended and taking advantages of loopholes in tax law by creating multiple shell entities around the globe. You can argue they have a duty to shareholders to optimize profits, but let's not pretend it's the same thing as paying your taxes as the law intended.
As a US citizen you can't declare your income was earned in Ireland and avoid or reduce paying US federal income tax. You can't avoid US federal income tax even if you lived in Ireland and worked for an Irish company for that year.
You can't just renounce it. It's a quite expensive process. And naturally, once you have, you no longer receive any of the benefits of US citizenship. Whereas the companies in question get to avoid taxes while retaining the benefits of being located in the US.
They're not doing business with another company in any meaningful sense. There's multiple companies set up with the same owners so they can pretend the one in the lower tax region makes all of the revenue, often through IP licenses that look like expenses to the entity in the higher tax region. It's financial engineering that doesn't reflect where value is actually being created or revenue captured.
I'm not a CPA, but my understanding is as a US citizen, your closest analog would be setting up an irrevocable trust. But, then you no longer have control of those assets. Owners of these shell corporations are able to effectively control their assets. Naturally, if they were legitimately doing business with a 3rd party company, they'd have no say over what that other company can do with their revenue. That's a key difference between what's a normal business operation and what's a shell game for tax avoidance.