anti monopoly actions != weak economy
Actually the opposite monopolist (and oligopoles etc.) tend to sooner or later stop innovating (they don't need to, they win by default) and decay into customer abusive absurdity. And to some degree we are already seeing this with alphabet.
What such concentration of money also means, is a concentration of power under the hand of a few people, wich then can use that power to e.g. undermine or outright destroy democracy, force countries to make really bad decisions (including economic ones), destroy industries "on a whim" etc. Worst huge economic crisis tend to long term make the richest of the rich even more wealthy and more important tends to open doors for even more power/abuse, exceptions in laws, state subsidization etc. So you can't even rely on them not intentionally fucking up their countries economy because "that would be bad". Not for them, at least not long term. And tbh. at the net worth we are speaking about "it being bad" still means they can live in luxury for the not just the rest of their lives and have multiple millions left to inherit to their children.
> know (academic) international relations Realism.
or you not knowing less about economics then you think
> to counter China and keep Europe safe.
eh, the financial support of right US milliadaries of right radical political groups which want to both dismantle the EU (and overthrow democracy) in combination with US mono/-oligopols in combination with corruption & US political pressure, is effectively killing most efforts for local EU competition. Honestly this is likely doing far more harm in how much EU is "able to resist" China then any "safekeeping" the US does (mostly indirectly by protecting their own interests).