It wasn’t “the most random possible way”, it’s been shown multiple times that it’s a parallel to Roger who:
1. Doesn’t let other people shit talk his friends and crewmates
2. Refuses to backdown from a fight even against enemies he has no chance of winning against.
You can argue whether you think this is admirable or stupid but it’s not random. This has been a running theme in One Piece even in the first chapter with Shanks, the whole “you can make fun of me but you can’t talk shit about my friends.”
Plus I think it’s a good (but sad) way to close Ace’s character arc.
He didn’t become a pirate to become the next Pirate King. His whole life he’s been searching for his purpose in life and to know if he deserves to be loved. He finally found both right before he died. WB gave him a place where he belonged, showed him that he deserves to live and be loved. And in return, he wants to protect WB’s name and legacy with his life.
His death was also necessary for the plot since it’s the catalyst for the time skip because it made Luffy realize that he needed to be stronger. He can’t always rely on sheer blind faith. This also made the crew become more equipped to take on the New World and become the future Pirate King’s crew.
Marineford was the peak of Oda’s writing.
As for the other points, yeah Oda realized he fucked up and added Sabo. But I guess he’s got that revs thing going for him.....
And characters not developing is just more of an overall One Piece problem than just pinning it down to Ace’s death. In fact, post MF arc was one of the instances where we’ve seen Luffy develop and reflect on himself.
Meanwhile now with Wano etc, he’s just doing the same thing over and over again.
I’m going to solo Kaido > gets knocked down by Kaido > many chapters later > I’m going to solo Kaido > gets knocked down by Kaido again
I agree with Kiwi.
Although of course, I still think that death was somewhat hasty, but as time passed I have understood that Oda didn't find another way to kill him, and that was something that marked Luffy (and other manga characters, and many manga readers also)
And I know that several here are going to get angry with me (sorry
@Finalbeta 
) , but it is the first time that I'll give my opinion on this (sorry this testament):
@Charlotte Sky , I can find you some reason about Sabo, about the fruit and about the physical appearance, although the personalities between them are different. Okay, Luffy and Ace share qualities like a feeling of justice, fighting for freedom, and of course, recklessness as part of their personalities. Sabo also shares those qualities. Also that anger that they cannot control when they see an injustice. Sabo got upset about Burgess and Kuma. And no, I'm not criticizing that they're reckless, it's part of the personality of the three. What I'm trying to say is that it seems that Ace is often criticized more for recklessness, more than his brothers and other characters in the manga.
Although I have respect for Sabo, I'm not his fan and I don't have affection for him (like other characters), but I also don't hate him (I felt sorry for him when he remembered Ace after knowing his death and when it was theorized that it could have happened to him something bad in the Levely) Of course, I think his reappearance is a bit forced (personally, I think it would have been better if Oda introduced him a couple of arcs before maybe), but ok, it's acceptable within the plot, because he's Luffy's brother. He loves Luffy, he is a brave character, strong and committed to his cause. And I think it's good that he is a revolutionary, because in the flashback there were all indications that the path he was going to take would be to join the revolutionary army.
And yes, I don't like is that Oda gave the Mera-Mera no mi to Sabo. I understand the theme of "inherited wills" in manga, but I consider that being a user of someone else's fruit doesn't make you carry their will. Several characters have carried the will of others without having any fruit. I have read several comments in different places, about the Mera-Mera, saying that she was wasted by Ace and that she had to get more in the manga...
By giving the Mera Mera to Sabo, in part I feel as if Oda implying to the readers that "Sabo can put that fruit to a better use than Ace gave him, so don't worry, all of you will continue to see the Mera Mera no mi in action". So, a certain part of the fandom comes to compare both in terms of strength and since they have the argument of the devil fruit, most of the time Ace is trashed, for the same old themes: "that he didn't have haki, that he did not know how to use the fruit, he was weak, he never faced people of a level ", and then took up the subject of personality as an excuse, when in reality many were disappointed by the character because he wasn't strong enough like them they wanted or hoped, and then they began to hate him.
And I repeat, my opinion is personal and I understand that everyone has characters that they like and others that they dislike.
Maybe when I re-read the manga sometime, I will reconcile with Sabo and other characters.