And just to be clear, they didn’t cancel the show, he chose to end it because he didn’t want to repeat/milk it. His job was done, he got 'em all.

Jeremy Wade, son of Poseidon

He’d have a decent shot against many of them because they lack the brain power to conceive of the idea that something topside is messing with them. The instant they have the mind or physical ability to check, it’s bad times for him. Better have centurions ready to defend him against the odd peeking plesiosaur.