I mean the DT770 has a measurable difference of about 8dB more than the THX00 PH at 10kHz, I mean I don't know what to say if you can't hear that, cymbals should cut much sharper on the DT770 than the THX00 PH. Those are relatively similar sounding headphones, as far as headphones go though overall, it's not going to be a stark difference. You can get to a similar endpoint with a lot of different methods. You can make a plastic cup headphone sound similar to a purpleheart cup, if you make other compromises to the rest of the design to compensate.
To put it in terms that may make sense to you, it's like if you take a maple-capped superstrat, you usually pair that with warmer pickups, while a basswood strat will typically be paired with chimier pickups. It's not that the wood didn't make a difference, it's that the designer compensated. Or the designer could decide to go for a really bright, cutting guitar, with a maple fretboard, bright pickups and a brighter body wood. With guitars, the designers are more or less unrestrained int he tone they can seek, because there's not a clear guiding reference point.
With headphones, we are talking about subtle flavorings, that absolutely exist, but are definitely subtle, because there is a standard of seeking some amount of neutrality (unless you're making Beats). And, again, this has all been measured and replicated by multiple non-affiliated people with measuring rigs. ANd if you listen critically enough, you will certainly start picking up on the differences. Since you play guitar, ask any engineer you record with if the speakers or headphones they use to mix and master can make things sound different, Every single one will tell you yes.
I don't care if you don't think cups resonate. They do. Not a ton, but enough to create different tonalities. Some designers aim to totally cut out resonation, some aim for euphonic resonation, some just sort of do it by gut. You brought up the TH900 before, they use a more resonating wood, but they also damp them with dynafil to cut down on midrange resonance.
My guess as you get more used to the differences between the THX00 PH and DT770 is you'll start hearing the differences more clearly, especially that huge spike the DT770 has at 10kHz.