Who cares about the off season success that Marvin has had, it makes no difference aside from confidence. If your a true fan you will have seen the obvious aggression and speed difference between from his rookie 450 year (2016) to his sophomore year (2017) indoors and out.
His 450 Supercross career so far is very comparable to his 250 Supercross career. His first year (2012) he looked stiff and timid and although close didn't capture a win just like in 2016. Second year (2013) once he figured it out he won 4 of the last 6. In his third year (2015) he dominated the championship winning 6 races.
In 2018 I see Marvin getting great starts, being very consistent, winning about 5 races and being competitive for the title.