It’s just a matter of distribution. How many bitaxes are out there and how many s9’s are there.
You can run the numbers. 10 bitaxes give you 5TH, will be thousands of years between blocks.
Discussion
Agreed, thousands of years to find a block but remember there is a randomness on who wins the next block. By joining a small pool of ten bitaxe miners you increase your chance being one of the lucky winner while still maintaining the chance for a big pay.