To answer the bolded, because to have both Sterling's off the ball movement and pace is an extraordinarily rare combination.I never mentioned Jack Harrison, so not sure why you quoted him. Why cannot a more technically gifted player be as prolific individually or making the team more prolific?
Sterling has sensational movement; I'd rate him as the only player we've had that comes close to what Silva had in that capacity. His timing and ability to be in the right place at the right time is standout. Add in his pace to get to where he needs to be a yard faster than everyone and it adds up. It's like Muller at Bayern Munich.
Unfortunately, you can't coach that movement so easily. Silva had it from a very young age, as did Sterling.
The only way a more technically proficient player could match Sterling's output from the wings in our team without that elite movement is if they have absolutely elite technique. Maybe Foden could get there, but it's been a bridge too far for the likes of Sané, Mahrez, and Bernardo so far.