The Baby Bell breakup was 36 years ago, resulting from antitrust action brought 46 years ago. Moreover, AT&T and Verizon have consolidated six of the seven Baby Bells into the 2 companies.
But it left the local monopoly in palace instead of mandating Local Loop Unbundling which is why the US and Canada has such poor competition for highspeed internet.
2 is still more than 1, and there was a lot more competition in the intervening decades when there were more than 2. So it sounds like it worked for the most part? Certainly more so than doing nothing.
The issue is that the baby Bells were allowed to reconsolidate at all, or allowed to avoid competing in other provider's coverage areas. I agree some good came of the breakup, but the hands off position taken by subsequent administrations has allowed most of the Good to get undone.