Most importantly, contracts need to be written down — proving that an unwritten contract exists, what its terms are, and if they are enforceable is extraordinarily difficult, and courts do not like doing it, especially for ultra-sophisticated parties with a long history of dealing.

this isn’t negating the point, it’s explaining the point: they need to be written down, here’s why. it’s like saying someone needs to train for a marathon to run one, because otherwise it will be very hard to avoid muscle damage. there’s no logical necessity but it makes sense as a practical claim