First off, I'm not saying this is a 100% thing that happens every time, I couldn't fit "many times" in the short title slot. But when you look at top fighters it has happened.
The most famous two that come to mind are HW champ Stipe Miocic losing to LHW champ Daniel Cormier and LHW Forrest Griffin losing to MW Anderson Silva.
I said this in the past before both fights happened, Forrest Griffin and Stipe Miocic are Jack-of-All Trades Master of None fighters. They're like jobbers. They usually have great conditioning (which helps them wear down their opponents), decent chins, and are fairly decent at all facets of MMA, however they lack the lethal skill of either deadly striking or ground game. They aren't 1 hitter quitters with feared striking like Mark Hunt or BJJ wizards with fight ending subs like Demian Maia. Fighters aren't afraid to stand with them or go to the ground with them.
If a Jack-of-All Trades Master of None fought another Jack-of-All Trades Master of None from a lower weight class they would most likely since but since their lower weight class opponents have lethal skills they lose.
When you look at Forrest's and Stipe's record you don't see consistent 1 punch KO's or subs against high level opponents. (Sure you see Stipe's 1 punch KO of a stupid Werdum who ran chin first, hands down into Stipe's fist, but Henry Cejudo could have probably KO'd Werdum running into his fist that day). This is why Anderson beat Forrest, Forrest wasn't a great striker and didn't have 1 punch power but he chose to stand and bang with Anderson, but what else was he gonna do, take him down with his mediocre BJJ skills, and lose with 1 punch. And you saw Stipe lose to a smaller fighter who has more punching power than him. You could even throw Cain Velasquez in here. He doesn't have lethal ground skills or 1 proven 1 punch KO power and normally tires his HW opponents out, it's not hard to gas most HWs, before the inevitable TKO victory. His only 1 punch KO was a battle-worn Big Nog's who's chin was already gone. I also said earlier that if DC and Cain fought DC would win because he has a better chin, superior wrestling, and heavier hands. Once again a case where the lower weight class fighter would beat the heavier weight class fighter, DC the LHW beating Cain the HW. I will note that DC initially fought at HW but that was almost 1/2 a decade ago.
Look at GSP vs. Michael Bisping. GSP the WW beat the MW champ Bisping with a sub. GSP hasn't used a sub in a long time but he has a very good sub game and is lethal with it. Bisping, who's a great all around fighter with great conditioning does not have lethal 1 punch power or a great sub/GnP game and we saw what happened there, Bisping got sub'd in a dominant loss to a lower weight class fighter.
When you see high level fighters who lack a lethal skill such as proven 1 punch power or a lethal ground game you have a good chance of seeing them lose to a fighter from a lower weight class who has said lethal skills.
Agree/Disagree?
