For instance, if we can reasonably assume an acquisition will lead to the potential for future harm through accumulation of power, influence, data, etc, that should be sufficient to block it.

Mergers are in and of themselves simply recognizing an efficiency of scale. It should be possible for a business to achieve success without that shortcut, broadly speaking. Once they're big enough already, that is.

This seems to tie in nicely to the recent narrative that efficiency is the opposite of resiliency, and that maybe not all efficiencies are good.

Much smaller companies used to get split up, but with globalization our understanding of what a large company or what a monopoly is changed.

When it comes to these things countries nowadays are more hands-off than they ever were. Further, advocates of these 'hands-off' approaches like to pretend we'd be returning to some ideal of old that brought prosperity and countries 'meddling' in the 'free market' is some modern fallacy, which is just revisionist history.

Edit: While the above is more personal observation than based on any hard data, there appears to be research supporting my position. This is looking like a good overview: https://som.yale.edu/faculty-research-centers/centers-initia...