Trout is undoubtedly the best player of this era, and arguably the best non steroid player since the days of Mays, Mantle, et al.
If he keeps his pace up for another eight years, he will be right up there with the all time greats, excluding only Babe Ruth.
But to give some idea how good Mantle was ( on one good leg)...
In terms of fWAR, Mantle had three seasons better than Trout's best...two by a lot.
In terms of OPS+, Mantle had three seasons far better than better than Trout's best.
In terms of wRC+, Mantle had five seasons better than Trout's best, two by a lot.
Unfortunately for Trout, he will not get as big of an opportunity to shine in the post season as Mantle did.
Mantle's alcohol use, general life style, and career full of injuries are well known, and had to negatively effect the length of his career, and his later production.
By all accounts, Trout's lifestyle is more attune to a longer and perhaps more productive later career.
When he was about 10 yrs old, my cousin got to see the Tribe play NY in a Sunday doubleheader. The old stadium was sold out, and he and my uncle stood behind the centerfield fence. Right in front of them was the Mick. To their left was Maris. To their right was Yogi Berra in one game, and Elston Howard in the other.
Can you imagine that?