All of your points ring true to an extent. Players can be on a hot streak and continue that trajectory (Kante being one), but it's more often than that it ends, and you truly see where the player is at.
The last point is something far too many fall foul of when silly season comes around and think we ought to be in the mix for said player. As you stated, we need to find the next big thing before they become superstars. Shame we didn't see it through with De Bruyne & Salah, to name just two.