Let's say McDavid ends up being a faster, higher scoring version of Crosby and Eichel ends up being a more physical, faster, grittier higher scoring version of Toews.
Being an avid college hockey watcher (mainly for Oilers interest, not the interest of the college game), I can tell you that Eichel's 2 way game and grittiness is vastly overrated. His skillset is outwordly but he's a pure skilled player, he's not going to dish out hits on the regular and he doesn't battle physically along the boards, at least not consistently. He also floats defensively, really needs to work on his play away from the puck IMO. I actually think McDavid is more polished with his 2 way play while Eichel is clearly more physically mature.
Where his strength lies is in his powerful stride and using his long reach to protect the puck plus his hockey sense is elite, up there with McDavid in that regard and has an excellent, accurate shot.
What's he's not is a physical force like Getzlaf and he's not a 2 way stud like Toews. He reminds me of Modano stylistically.
I'm sure that his 2 way game will improve because he's such a smart player but it's not there yet.