His talent to score goals is a fact and proven over a number of years. Only two other players in the league has proven to do this better.
Which metric are you talking about, here? Total goals? Goals/season? Goals/minutes? Because he's not third best on any of those categories right now. Furthermore, here are his goal tallies since WBA:
12/13: 17 goals for WBA
13/14: 15 goals for Everton
14/15: 10 goals for Everton
15/16: 18 goals for Everton
16/17: 25 goals for Everton
17/18: 16 goals for United
18/19: 8* goals for United
Apart from that 16/17 season, he's never crossed the 18 goal mark in the EPL. You have called his last season 'Beast Mode' where he scored 16 league goals for us. For reference, here are the EPL goals of our main goalscorer since RvN:
01/02: 23 - RvN
02/03: 25 - RvN
03/04: 20 - RvN
04/05: 11 - Rooney
05/06: 21 - RvN
06/07: 17 - Ronaldo
07/08: 31 - Ronaldo
08/09: 18 - Ronaldo
09/10: 26 - Rooney
10/11: 20 - Berbatov
11/12: 27 - Rooney
12/13: 26 - RVP
11 of those 12 seasons, Lukaku's 'beast mode' would not be good enough. The only season in that list he'd get into with 16 goals is the only one where we didn't win anything - 04/05.
He cannot be written off while he's still 25, but you have to agree that he needs to turn around his fortunes in an extraordinary manner to establish himself amongst names like RvP, Rooney, Berbatov, Ronaldo or RvN. There is a great gulf in quality between those names and a striker who as of now cannot judge the flight of a long ball, or control it when he finally manages to stand in the right place to receive it.