Don't get me wrong. I'm not suggesting that Kane and Weghorst are roughly equally proficient goal scorers. Such an insinuation would be madness of the highest order.
I was responding to the hypothetical question that if we had brought in Kane during the January window whether our record of wins and losses would be all that much different than it is. I'm going off memory only but I don't believe that since January 1 we've lost many games narrowly where a single goal by Kane would have scraped an equalizer or the match winner. There was the 2-2 draw with Leeds and the 1-1 draw with Palace and of course Arsenal beats us 3-2. But let's say that Kane would have scored in each of those games...would we really be in first or second place as a result? I don't think so.
We definitely would have won the games we did win by more comfortable margins and there's of course real value in that, but winning by 4-0 rather than 2-0 yields the same three points.
But let's go back to the matches in the PL since January where we dropped points. Even assuming Kane scored in every one of those games, which is not unreasonable, I'm not seeing enough points clawed back from those matches to have put us at the top of the league by now. That's the point I was trying to make. There's obviously no comparison between the undisputed world class of Harry Kane and the limited positive contributions that Martial and Weghorst have given us since January.
What you said is like describing Kane as Weghorst with goal. You completely disregard the possibility of different outcome of result from having better performance.
Games like Leeds home, Liverpool and Newcastle, Weghorst were especially bad. The issue is not only about not scoring, but also about him failing tactically. In these three games, ETH tried weird formation to shoehorn Weghorst into the team with negative effect. Against Leeds at home, it was Rashford on the right, where Rashford up top would easily deal serious blow to Leeds high defensive line and they don't know how to defend different. I took 0-2 before Weghorst was taken off and Rashford was moved up top. Against Liverpool, Bruno was moved to the left and couldn't influence the game. Weghorst played as no 10 which he offered nothing before coming off after Liverpool went up 3-0 which pretty got the game in bag. Against Newcastle, McTominay with his scoring form for Scotland was put in no 10 position in hope that he may score. Sabitzer with Bruno playing deep was outfought, while McTominay and Weghorst posed no threat to Newcastle defense.
If we have Kane and set up with Kane up top, Rashford on the left to exploit TAA defensive zone, Bruno in his natural position, we might have played better overall, and likely scored before Liverpool could get their way and killed the game. There is every chance we didn't lose by that scoreline. Even getting a point, or a victory if Kane was clinical in place of Rashford that game. He didn't need tap in chance to score as we see how he navigate to score goal from opening further up the pitch in Tottenham Newcastle game. Newcastle got the second goal when ETH got desperate and made questionable change at the back which allowed them opening to kill the game. If we have a proper CF, and someone who is known to be a playmaker too, we may have prevented that situation, to get at least one point.
Then we have game like Crystal Palace away, Southampton at home where Weghorst receive chance where someone like Kane might have scored. Sancho would have been subbed off after Casemiro sent off instead of leaving a non performing player on because there was a worse player in Weghorst needed to leave for McTominay. It's not only about scoring. It's also the level of control when you pose a bigger threat to opposition. Playing Weghorst most of the time have the opposite effect on us.
2 point extra here and 1 extra point there, if you add up, we have 8 extra point (2 from Leeds, 2 from Crystal Palace, 2 from Southampton, 1 from Newcastle, 1 from Liverpool. And I am not counting the Arsenal potential one extra point), we're back to 3 point behind Man City!!! May not be enough for us to win the title in the end, but that margin is enough to put us a title challenge which is higher than anything we had been post SAF. Further fine tuning and improve result the whole season and we're talking about winning the title.