If Tammy were to continue scoring at the rate he has so far in his career then he'd hit 238 goals at club level by the time he'd played the 531 games that Lukaku currently has. Lukaku for comparison has 259 goals at club level. It's worth noting that Abraham scored 51 of his 105 goals so far at Championship level. Lukaku got 41 in Belgium. I actually think Tammy is similar to Lukaku in that his technique completely abandons him sometimes and he looks ungainly a bit too often. I think the main difference is that Tammy puts a good defensive shift for his side and is more mobile.
That said, I think people are over the top with their criticisms of Lukaku. I don't think he's truly elite or world class but his scoring record at club and international level is excellent and he falls into the bracket just below. Part of his quality is that he's never injured. His appearance record is fantastic, he's played in nearly every league game when he's been a XI player since the start of his career! He's not a player that I enjoy watching but he's had an incredible career so far. His numbers by the end of his career will be up there.
As you can see in the FBref scouting reports Tammy defensive stats are in the elite bracket whilst Lukaku's are quite the opposite
https://fbref.com/en/players/f586779e/scout/365_euro/Tammy-Abraham-Scouting-Report
https://fbref.com/en/players/5eae500a/scout/365_euro/Romelu-Lukaku-Scouting-Report