This would’ve been at a time when people didn’t realize how differently HpTF can trend between rig ears and human ears. Driver size is a parameter that can influence a lot, but the end result is what matters not the fact that it’s a specific driver size. This is a matter of necessary and sufficient conditions.
With that said, you may come across things like deep phase cancellations, and while it’s exceedingly rare, there are also some situations where headphones aren’t minimum phase. So the possibility of driver-based limitations and various other design issues can lead to anomalies.
I think this is in general a good outlook to have. Though I do think the FR graph is useful as an initial guideline. It won’t tell you how it sounds to you, but it does tell you how it could sound to any given person. That’s better than nothing.