If fuel comes out of tank unrestricted,.. through the fuel line, or the vac line... it flows everywhere below the tank...
The first test, should always be the petcock...(because it is a known issue)...
Once that is ruled out... the next test is the float system...
It's also the easier thing to rule out... (if everyone would just do the proper and complete test)... which includes both setting to Prime, and blocking the vac line...
(So many people just turn to Prime without blocking the vac line)...
There is no definitive test for a float problem... it's trial and error...
Leaky floats,.. sticky mechanism, worn seat, hardened needle tip, grit...
Test the petcock first... it might save pulling precious hairs out...

...
Once the pet is ruled out, you might well well be right, Steve...
It's a 50/50 proposition...
It's just best to try the easiest test first...