Valtteri Bottas has recalled how the ‘most difficult year’ he spent at Mercedes left the Finn with a point to prove in Formula 1 and it returned the ‘best’ season of his career. The current Sauber star spent five years at Mercedes from 2017 to 2021 as the teammate of Lewis Hamilton. It marked the only time to date that Bottas has spent consistently at the top of the Formula 1 grid after starting his Grand Prix career at Williams during the 2012 season. Mercedes turned to Bottas when the Silver Arrows suddenly had to seek a new driver on the back of Nico Rosberg retiring straight after he won t…