Regarding the bold:
1.) To say that D's inspire people to be better people is false. People may want to become better people after interacting with Luffy maybe, but there is zero evidence that people wanted to become better people after encountering Ace, Garp, or Roger, and certainly not Teach. The only single consistent trait that all D's share is the will to live the way they want to. Other than that, your statement regarding the tendencies of D's is wrong via lack of evidence. Luffy's traits do not equate to the traits of all D's.
2.) Law isn't Sasuke, his popularity goes beyond his looks.
3.) Law is pretty important to the plot, considering they are in an alliance to take out Emperors, and he in no way disrupted the formula of the series. In fact, his presence reinforced the pattern of the series, as it has never been just the straw hats alone during any story arc.
1) I think Ace's last words to Luffy were really hard hitting and had an enormous impact on Luffy which led to Jinbe telling Luffy him to keep on living because he still has his friends. Ace's death and legacy had a huge impact on Luffy's way of living. Dragon could literally change the world and is inspiring people to question the WG. Saul told Robin to keep on living and that she won't always be alone and died smiling. We haven't seen enough of Garp. Blackbeard literally gave one of the most inspirational speech to Luffy when they met on Jaya about people's dream never dying. Roger was clearly admired by his nakamas (just look at their reactions) and even by his rivals and inspired Shanks the most by giving him his hat.
2) He certainly is not Sasuke (who could be as bad anyway). Well, Law was extremely popular even when he was just barely introduced in sabondy and we knew kitten about him. I think people were just in love with his design and bad boy personality but at least one girl admitted that she was mainly attracted to him for his looks and not really as a person. Unfortunately, there are people who voted for characters like Rebecca and the giant mermaid for their huge pillows and nothing more (One Piece Podcast goes to Japan). I preferred Law when he was in a Han Solo type of character with his own Chewbaca. I thought that he was better fitted as a cool and laid-back badass and he kinda became too serious in the timeskip cause they likely wanted to give him a bigger role into the story.
3) I just feel that Law being side to side to plan stuff with Luffy takes away the role of Nami and Zoro. The issue is that I don't really feel the friendship between them cause it was not developed enough for me to care. In contrast, I mean we really get to see Nami and Luffy grow as friends (they bicker, they have fun, she learns to know luffy and see that pirates are not all bad) culminating to the girl asking for her captain's help. I feel Law and Luffy lack these kind of moments for him to be put in the foreground at the place of Nami and Zoro. PH was too much about Law and should have been about Luffy becoming more and more friends with Smoker. Nami's possible friendship with Tashigi could have given the orange girl some great moments and seeds of having marines rebelling against the WG. I just felt that PH would have been great character development for Luffy, Nami, and Zoro but it ended up too much about Law and the story felt more like his own.