Hmm. Unless somebody asks Jim Kaposztas (the creator of the first intentional AMV back in 1982) directly, I don't know if anyone can claim that MAD led to AMVs. Sure, they look the same and they both use Japanese-origin media as their raw material but that isn't conclusive. More importantly, they had completely different intents when they first developed.
MAD movies started as a remix video art that was sometimes nonsensical, sometimes a commentary on the state of culture or politics (satire or parody) but MAD movies weren't necessarily trying to tell a story.
Anime Music Videos are (were) about telling stories using the music to emphasize an element (an idea, a character, or a story) from the anime. You got props for editing a song and video that was synched to one of these elements. During its heyday, AMV competitions were very much about staying true to this formula. I haven't been involved in the AMV community for a number of years now so things may have changed.
I'm going to
undeadpool the AMV entry and open it up to debate again. If MADs is confirmed, what makes AMVs not notable?
I'm also going to try to contact Jim Kaposztas and ask if he had seen any MAD tapes before he made his Space Battleship Yamato AMV.