A single character "holding his own" against Juggernaut is still a pretty big feat. 80's Spider-Man was also facing down villains such as Mr. Hyde and the Wrecker and his Wrecking Crew, characters originally designed to give Thor a bad day. Spider-Man has also held his own against a team of X-Men on a few occasions and a Spider-Man robot duplicate created by Kang trounced the Avengers (Cap, Thor, Giant Man And Wasp) only for the real Spider-Man to show up and save the day. Maybe you are just seriously underestimating the ol' Webhead?
And if I remember correctly, wasn't the Spider-Man/ Firelord fight followed up on in an old Avengers comic? that may have shed some light on the issue.