You're right. For the argument for the other side, the top four largest banks—JPMorgan Chase, Bank of America, Citigroup, and Wells Fargo—collectively hold approximately 43% of all deposits in the United States, and in some ways they are self regulating or have a revolving door with their regulators. But we certainly have a lot of banks and anyone can buy a small one and give the banking business a shot.
US has more banks than any other country by a factor of 10.
https://www.helgilibrary.com/charts/what-country-has-the-mos...
And #4 for branches per capita: https://www.theglobaleconomy.com/rankings/bank_branches/
7x as many branches per person as Canada
Sure, those data sources are a bit sus, but I'm sure they're relatively correct. And dunno how credit unions play into it.