On the right track with this. There are only 170 MM working adults in the US amd a majority dont have retirement plans think low wage jobs/agriculture/PT and contractors. And there are only 60 MM retirement accounts in existence in the US. Can't use total population where well over half aren't working due to age/retirement/disability etc. So that number for Fidelity represents only 1.7% of retirement accounts.Not to mention...Fidelity might be the largest, but isn't even holding 100% of that 350m anyway.
Ascensus, Empower, Alight Solutions, Vanguard, Principal, TIAA, Schwab, ADP, John Hancock, etc. etc. there's probably hundreds if not thousands if you really find every single agency/group that helps with planning for folks.