When you move up from one weight class where you have been previously fighting to another, be it boxing or MMA, its called moving up a weight class. Conversely if you go down its said you are moving down or dropping down a weight class. Last week of the prep it was decided Conor would move up 2 weight classes instead of 1.
The lack of weight cut for Nate was a huge advantage especially with the late call up. Doesn't need explaining.
Yes we will probably never know about how he fairs against other gatekeepers at 155. I think pretty well though Conor would never have to go through them anyway. Nate was a unique case because of money. Of the top contenders vs prime Conor, Ferguson he annihilates imo, sitting duck in the same way Gaethje and Lando put it on him but far worse. Gaethje would be interesting but again good chance of being lopsided because he is not an offensive wrestler. Poirier the renaissance man? Has a chance to win of course but he wouldn't be the betting favorite and its not like any version of Dustin was better than the Conor that fought Alvarez.
You can use technicalities but we all know he's a natural LW, especially as he's said it himself and he fought a guy whose also a natural LW. Saying he "jumped up two weight classes" is something people do to add sprinkle to his achievement. If you want to do that then fair enough.
As for Nate having advantage for no weight cut after getting the fight late, surely McGregor didn't need to weight cut either when it was announced it will be WW fight?
As for your final point, I think you're doing way too much MMA gymnastics, especially as you yourself said styles make fights (I think you said that?).
Ferguson does get dropped but he's durable. If McGregor can't finish him quick, he'll have the same fate as he did against Diaz. Ferguson can also take him down and choke him out. It's not as clear cut as you make it sound.
Gaethje isn't an offensive wrestler but that's not the only way to win. Gaethje hits hard and has a good gas tank and is also durable. Against, McGregor, Connor would be favourite for the first two rounds then the tables would turn. Not as clear cut as you make it.
As for Poirier, he's not the same fighter at LW as he was at FW. He was even close to submitting Khabib. It would not be the same fighter as before.
You're comparing against prime McGregor... So compare to prime versions of these fighters and you'll see that these fights can go either way.
Like I said, no way of knowing until it happens.