This is correct when speaking short term. Putting on weight and moving up, or just simply moving up without cutting, often won't end well. You're not used to fighting like that. See Holloway jumping up against Poirier where it just very clearly was a LW vs a FW as Poirier had long adjusted to LW while Holloway just moved up.
Jones isn't saying he's doing that though. He's putting on the weight slowly, then re-adjusting to the size, and only then going into camp for fighting. Hence why it's Stipe vs Ngannou in March, not Stipe vs Jones in March. By the time Jon fights, he will be used to working at HW. He'll have had probably 1+ year working on this transition.
I overall agree Jon would probably be better as a 225-230 HW who tries to be much faster than them rather than trying to nullify some of their strength and size, but I'm also fully expecting him to come in actually ready to fight at whatever weight he shows up in. His record and status mean far too much to half ass that. People criticized GSP for the years he spent working to MW, and while his tank didn't seem quite what it used to be, his strength and power clearly did transfer correctly by taking that time to do so.