1. Shakky commented that every Supernova would have had to go through difficulties that were like the Strawhat's, meaning they would have needed similar growth in order to overcome them.
2. Based on personality and possession of Haoshoku
3. Because he was Dragon's son. Akainu didn't care about who Luffy was specifically, he called him "Dragon's son" almost every time while referring to him, and targeted him and Ace for, and he said this reason himself, "the blood he carried." Akainu said even if everyone else escaped, he wouldn't let them get away, meaning he would try especially hard for them as opposed to the likes of Marco, Ivankov and the other commanders. It had nothing to do with Luffy's strength.
4. Because Whitebeard liked Luffy and because he was the last remaining remnant of Ace's will. Once again, not because of Luffy's strength.
5. That's a legit point, he had good genes
6. Good enough a point
Charisma, being similar in personality to Dragon, and having Dragon's blood isn't gonna help Luffy in VS matches where the opponent is dead-set on defeating/killing him.
Luffy and Law are more or less on the same level. Luffy can punch harder and has more durability. Endurance is a tricky area, is Law inferior because his DF drains him, or are they even because he can continue fighting while close to death and despite his DF constantly draining him? Other than that, their capabilities are more or less at the same level. Luffy can cause more destruction, but that's not all that matters in overall strength. If you're determining who's stronger by who'd win in a fight, it can go either way, but Luffy's fighting style puts him at a disadvantage against Law. For example, Gear 4 can do heavy damage to Law, or Law can take advantage of Gear 4's build-up rather than standing and watching like Doffy did, and cut him before he even has a chance to go full Bounceman. Law has shown to be able to keep up with Gear 2 during the Red Hawk tactic and the Gamma Knife tactic via Shambles, and Gear 3 has too many openings(this is the worst thing Luffy can do while fighting Law).