As I clearly stated, two of the three forwards were "prolific" before joining us & Morata had decent numbers too. Whether they flopped or not has nothing to do with us not signing players.
United have been without an actual top-quality CF for years, and using one of the best players of this generation to justify them striking gold is hilarious. To add to that, CR7 has all but left, so who's their quality CF you alluded to, Martial?
With regards to Arsenal, Aubameyang's goal return over the last two seasons was 14 in 43 league games. He started off well, but went downhill & Arsenal only had Lacazette to rely on. Now, going back to your original post, who's the quality CF in their ranks now, Jesus, whose goal return is 17 in 57 EPL games?
I don't think I need to say anything to debunk your "Big 6" statement.
Conte got rid of the gold we found. The lack of decent scouts is why we've failed to sign another Drogba, Costa or even an Anelka. If we sign a CF that is stylistically a good fit for how we play, chances are he'll thrive.