Fact is, just because corys often occur in hundreds in the wild does not mean they have to any more than humans have to live in huge cities ,
There is as much bad info on the net as there is good info. I do what works great and ignore what seems to be bad info.
Among other fish, I have 3 (panda) Cory cats in my well planted 10
gal tank and they do just fine.
BTW, this is also with a gravel substrate and the bad info says you can not do that either with Cory cats.