People are too used to having a space animal (or Falcon) involved in their matches, which generally make the matches shorter because they're high risk/high reward characters.
Most matches involving other character combinations last anywhere from 3-5 minutes. Then there's Peach/Jiggs/Samus matches which last even longer.
We've got a few PM characters that will fit into that spacie+Falcon time bracket. Matches involving ZSS, Ivysuar, Ike, Diddy Kong,or Lucario tend to not take very long in my experience.
Ledge occupancy seems to be the biggest factor for P:M matches being longer (it's harder to gimp people)
Another large contributing factor to PM matches being to long is the fact that momentum is not carried after techs in PM, while it is in melee. If you crouch cancel->teched something in melee you'd still have to find a way to counteract any remaining knockback from the attach, while in PM you just stay in that spot after the tech (and people accidentally do this quite often in both games, only in melee you'd die anyway after most of those, while in P:M you live)
There's also the idea that matches can get shorter as players get better with their characters. They learn how to combo more efficiently, how to edgeguard more efficiently (yes the opponent gets better at recovering, but for most characters this still won't compensate for the powerful edgeguarding of the other player), and how to punish mistakes harder in various situations.
Honestly I'm not too concerned with most of the new recoveries. If we ever get ledge occupancy, they'll all become much more gimpable (many of them are already actually. People just need to learn how to edgeguard with characters who weren't good in melee)
and i have no idea why you chose m2k and top players in the world as an example of someone technical when there are amateurs just as technical as m2k, hungrybox, mango, pp, amsah, etc
He chose M2K because he's often referred to as "a robot."