How much do you like MJ?

[Ozymandias]

Before and after Gwen died, Peter Parker's stories were action stories mixed with drama, comedy, and romance. Gwen's death did not in any significant way change the nature of the series and stories that could be told.

More like "the stories that were told". I could've told a completely different one, but then again, she wasn't an accessory to me. Conway on the other hand, though very little of her, so he tried to erase her as quickly as possible and to do that, she couldn't have a greater impact dead than she did while participating in the story. Not that it worked, hence the current conversation, as so many others over the past five decades.

The hard truth is that you can't kill off too many characters without changing the tone of the stories. Just as you can't bring in too many love interests, just as you can't keep bringing characters from the dead. The more you do that, the more emotional investment you drain from the stories. So in that sense, in terms of an ongoing serial story as opposed to selling merch, it cannot be truly said that long running supporting characters can be safely discounted and removed. It's important for a serial story to maintain a tone and style, and the way to do that is to keep hold of and maintain long-running supporting characters. More than the protagonist, it's them who maintian and uphold the emotional investment of the story. You can sell Superman and Batman toys without anyone knowing they are Clark and Bruce, but you can't tell the story of Clark and Bruce without the Kents of Smallvile, the Staff of Daily Planet, without Alfred the Butler, James Gordon, and a Robin of some kind.

In the case of Spider-Man, he lives in a fairly sanitized corner of the Marvel Universe as it is. Compare the tone of Spider-Man with Daredevil. Spider-Man has only one dead girlfriend with Gwen, but Daredevil has several, Wolverine even moreso. The criminal element in his stories don't touch on rape, molestation, human trafficking, and other kinds of stuff. The more death, violence, and tragedy you pile on, it becomes impossible to have Spider-Man be Mr. Quippy or whine about "Typical Parker Luck" without coming off as a sociopath when faced with the far greater suffering faced by people around him. You saw this in Mackie's run with Mj's "death/separation" thing. It made the titles really depressing to read and drove down sales. At the end of the day, Spider-Man is not the character who buries loved ones by the dozens (that's Daredevil, Batman), whose daily life is preoccupied more with the lives of people he fights than the ones he loves (Batman, The Punisher). So you can't really kill off major characters like Jameson or Mary Jane, and still pretend the character is the same as he was before.

I mean any other given character in her instead, not a significant portion of the cast or its entirety.

As a character, Gwen was totally peripheral to Peter's world. She wasn't close to Aunt May, in fact she bullied her. She didn't like Spider-Man and blamed him for her father's death, so that relationship had no future.

For six years, she was the girlfriend, and that was a big deal in the "House of Ideas". Relationships weren't casual, they mattered. If anything, too much.

Bullied? You mean ASM #109?

The character's opinion on Spider-Man was based on false information, spread mainly by Peter. At least she never shot at him, unlike his ever loving Aunt.

[...] have the original intended Lois Lane (MJ) waiting in the wings to play off a subplot that Ditko had set-up in his title, when she was the one Aunt May believed was right for Peter. So in a real sense Gwen's death was very much in the "illusion of change". It simply reset Spider-Man's status-quo to back where it was when Ditko left the titles

Ditko had that in mind? How did you arrive to that conclusion?