I felt the same about the Hal Jordan/Parallax thing in the 90's and let that fester for MANY years. My personal opinion is that MJ marriage just wasn't as important. There are WAY too many Spider-man medias where MJ plays little to no role in it... and zero medias where they are a happily married couple.. It's well known Marvel wanted it over... If it wasn't Mephisto than it probably would have a random mugging or cab accident.
ACTUALLY... If "I" were to write OMD that's how "I" would have ended. May gets shot... Peter moves heaven and hell to save her... Mephisto makes a deal to undo the stupid unmasking and bring May back for the price of ending the marriage. As soon as that happens, Time rewinds and Peter hears a shot, Aunt may does NOT fall... but MJ does. Parker luck strikes again.
I actually think I would have switched Mephisto for Loki maybe... but same principle. OMD was too open ended and had people talking years later. As much as Karen Page getting killed annoys DD fans... we don't harp on that killing any more. It's just something that happened and the character moved on...
It's that 'ghost' that keeps lingering around that people want to see undone that hurts the line.