Thats bullshit banks will not lend, if you have a property free and clear
Do hard money
They will do loans for any investor with 0 down, yes its is real. I have seen someone use them and flip 10 houses.
This is not always true in the current market. No comment on the rest of your post but I have a friend that owns rent property and flips houses in a similar manner. He has tons of credit, but he cannot buy a house. He owns dozens of vehicles, large equipment that cost $50,000 to $120,000, lines of credit for other things etc. He could go buy a fleet of vehicles tonight with only his signature but he cannot buy a house without a huge (30 to 50%) down payment. This is true of rental properties, flip properties and even a home for himself. He recently put 50% down to finance a property for himself, something that even broke idiots seem to be able to do with no problem.
Now I have no idea what exactly they are looking at that makes this next to impossible but he has great credit, makes early payments often but has had this problem for years.