I simply don't agree, no way he is anywhere near the absolute top in that department for me. In the end it's all semantics but don't see how you can argue him to be above any of the big 4 and then you have players like Bourque, Lidström etc who relied mostly on being in the right place at the right time.
To me Crosby is "generationally concistent" but his peak play is not all that special and there are like 2-3 players active at any given point in history that's able to match it(Ovi+Malkin from his own era somewhat proves this), contrast with McDavid who is a clear step above offensively atleast.
Why Kucherov is not "as good" defensively? If we take that as being true, I am not so sure I do, it could be due to the fact that Crosby is undoubtly more of a hustle type player that, atleast visibly, puts in more effort every shift and seems almost inhuman when it comes to keeping focus and put in the work.
Now Kucherov? He did infact outproduce McDavid not once but twice(and I would say it's more or less a fact that McDavid is on another level from Crosby in terms of producing points), he got the better raw totals in a season etc. If it's not due to hockey iq, then what is it? Of course era is part of it, in reality their peak seasons are somewhat close. Is he in your mind simply a more skilled player or what's the reason for him putting up, atleast, similiar caliber of numbers while having inferior hockey iq? Maybe Kucherov works harder? I would dispute that.