You're not saying "governments have interests" (which we can agree is obvious), youre saying the public principles invoked are contingent on whether they advance those interests and get swapped out the moment they don't. That's not a banal "laws protect interests", it's a claim about which interests and when the rhetoric changes.
"Window dressing" from the cited comment isn't about the existence of law, it's about the story told to legitimate a choice already made on interest grounds.
When a principle helps the home coalition's position, it's foregrounded, when it threatens it, it's narrowed, reinterpreted, suspended etc. The principle is the sales pitch and the selection and timing are about power.
Countries push openness most intensely in sectors where their firms can penetrate foreign markets (finance in the 1990s, software/IP heavy goods in the 2000s etc). Because openness abroad protects their capital, openness at home is celebrated until it starts eroding strategic capacity. Then come security reviews, export controls, local content rules, subsidies etc and everything is wrapped in principled language.
> Internal competition and level playing fields are promoted as they pressure companies to improve their competitiveness.
Until internal competition threatens a national champion in a strategic race. Then we let consolidation happen (or subsidize it) and call it "industrial policy". We laud the disciplining function of foreign competition until the foreign rival is big enough to discipline us, then it's "unfair trade", "security risk", "systemic rivalry" etc
For decades, openness to China was "win win globalization". As China's capability rose, the same flows (capital, tech, data etc) got relabeled as channels of leverage. Now we create controls, seizures/forced restructurings and targeted decoupling justified by a different principle than yesterday's.
So basically your "policy serves interests" is a truism that ignores the commenter's claim about how principles are instrumentalized. I mean free markets, antitrust, IP, security, sovereignty etc aren't a tight contradiction free doctrine. States pick the item that best advances leverage at that moment and explain it with whatever noble language fits. It's a realistic description of how advanced economies behave when the balance of advantage shifts.