I would disagree. I think it's quite obvious that higher body mass comes necessarily along with decreased coordination. It's reflected in statements like "he moves like a lightweight." What do you think does account for the clear difference in overall coordination and athleticism of smaller fighters? Here's an article I found after 5 minutes of googling that would seem to support this contention, though I must admit I'm way too tired to give it a proper read:
https://elifesciences.org/articles/07892
Statements like these come from the fact that lightweights are in fact very technical (compared to the big 205ers and heavyweights), though this saying also often refers to the speed.
That said, the saying doesn't tell us anything about the reasons why a 155er is on average significantly more technically sound than a 205er or heavyweight.
As for the study: either I'm a bit dumb now, or there is no correlation to out discussion about the correlation between size and motor skill, lol.
To my knowledge, the only reason, why bigger people are on average less technical, is because they are far less incentivized to care as much about their technique (as small people) to begin with; when Francis Ngannou trains with other people, he gets away with a lot of mistakes, simply because he's a mountain of a man, whereas Demetrious Johnson had no other choice but to work meticulously on his technique if he wanted to be able to not get his ass kicked all the time in training.
I also think that guys like Fedor, Gane, Tyson, (many other big boxers) as well as olympian heavyweight wrestlers and basketball players are good proof of big (and even huge) guys being able to move just as smooth/technically clean as small guys.
Last but not least: i'm not a fan of this "a-level athlete talk", but most guys in the NBA and NFL would be 205ers or heavyweights and many of them, especially the basketball players, have tremendous amounts of motor skill/coordination/talent in the former regards, so alongside the already small talent pool, it is kinda true that the majority of the crazy talented guys that size won't ever get into fighting (until fighters pay is better, at least.)
I think you get my maths, 198 lbs (average american male) is 33 lbs from 165 and 27 lbs from 225. 33 vs 27 is "roughly" in the middle. The average american is certainly fatter than the average fighter, but the average fighter certainly has more muscle mass. Overall, I accept your point though. 145 is probably closer to the middle of the body-size bell curve than is 205.
Oh, okay, fair enough to an extent.
I think the average american would probably fight at 155 - after getting in shape though, of course, lol.
wait a minute - who said "skilled"?

To me, it comes down to this: if you are born in a 165 lb body you are going to have a much higher speed and technicality ceiling than if you are born in a 225 lb body. All things being equal, therefore, to say you are a "better" fighter than a 205 lb fighter is to say that you perform better against your weightclass peers than he does his. in 165 lb bodies, everyone - your opponents and you, are going to be faster and more technical than 225 lbers. at 225lbs, you - and your opponents - are going to be more durable and stronger. It's not that either of these two attribute pairs are more impressive than the other as it is that they are more or less tied to their respective weight classes. Otherwise, we would see faster and more technical LHWs dominate and we wouldn't be so blown away by the abilities of Ciryl Gane at HW precisely because his technical abilities and speed are a rarity at HW, or even LHW.
it's just physics. What else would explain the wealth of technical fighters at lower weight classes?
I think this just hinges on our disagreement about the relation (or lack thereof) between size and technique.
In terms of speed, i do of course agree, that a 205er won't ever be as fast as John Dodson - but that's why i'm talking about technique! (alongside fight-IQ, tactics, etc. of course).
Like i referred to in another post of mine ITT:
Watch this striking exchange between Jon Jones and DC (the latter of which i rate very highly!) and pay attention to the lack of footwork, feints and striking defense.
A lot of what people perceive to be "brillian distance management" of Jon Jones has to do with the fact that a lot of his opponents, be it Rampage or Daniel Cormier, literally just plod forward in a straight line, making it very easy for Jones to consistently land straight-lined striking attacks.
Plus: look at what happened, when Jon Jones (in his prime!) faced a guy his size with good boxing and decent defensive wrestling in Gustafsson: Jones was in the fight of his life and though he won, he probably took more damage than he inflicted.
Look at what happened when Jon Jones faced Dominick Reyes (keep in mind that Jones, should we believe Anthony Smith, did at least until their fight, still fail drug tests): he lost in the eyes of most people.
I think Jones is a very talented fighter and has one of the best fight-IQs in all of MMA, but i also believe that he - more than any other GOAT-candidate - benefitted from fighting a lot of men who're not legit/natural (size-wise!) 205ers like he is and that's not mentioning the failed drug tests, as well as the fact that there are several GOAT candidates who fought more skilled /technique, fight-IQ, etc.) opponents.