Leaving aside that this article is written very much from one point of view, it's worth drawing comparisons with Argentina and things like the pari passu bond litigation. That statement is probably hyperbole, but there is a real premium to be paid if investors start thinking that there is more risk than expected to their investment.

On the other hand, the CJEU is basically right, in a sense of legal sovereignty that both the US and UK will recognize in their own ways: countries should not be beholden to foreign court decisions if they can at all help it. The EU has a court system, the CJEU is at the top of it, and its decisions should be final.

The real problem is the ability of countries to enter into agreements that promise some investor return that turns out to be against subsequent public policy or even entirely ruinous. The most egregious case was https://theconversation.com/when-even-winning-is-losing-the-...

(some more background, clearly translated from Spanish https://microsegur.com/en/spain-lost-four-international-arbi... )

Heck, I'm the beneficiary of such a scheme myself: I'm the holder of a legacy UK feed-in-tariff agreement that means I get paid about £0.15 for each unit of electricity I generate, regardless of whether I use or export it and regardless of market price. Until this year that was a substantial subsidy - as intended by the policy!