I haven't looked at any formal studies of the net effects of the Bell breakup, but I'd be hard-pressed to say they were net negative.

Especially with a relatively light "break-up, then allow to recombine as market evolution renders their previous monopoly moot" long-term approach.

Especially as Amazon is already many companies, in many different jurisdictions, and covering different product and service categories: https://opencorporates.com/corporate_groupings/Amazon

Spinning off AWS, which is pretty independent, might be enough.