That graph is for the D90 III Sabre DAC, but it seems you’ve forgotten to also include the same ‘THD vs Frequency’ measurement graph, as performed by Topping, for the D70 Pro Sabre DAC.
In fact, as per Topping’s own measurements the D70 Pro Sabre exhibits, also in that regard, worse measured performance than the D90 III Sabre, where a more pronounced rising with frequency can be seen, reaching 2x the THD @ 20kHz:
View attachment 352357
There’s one caveat however, the declared default PCM filter for each of those DACs is different. The owner’s manual clearly states that, in the case of the D70 Pro Sabre, the default filter is “F-1: Minimum Phase”, whereas for the D90 III Sabre the default filter is “F-3: Linear Phase Fast Roll-off”.
Assuming that this difference is not a typo from Topping, there should be a good reason for using a filter that doesn’t even provide a flat frequency response across the audible spectrum as default, which is the case for “Minimum Phase”.
It’s also reasonable to assume that Topping would choose whatever filter could give the best measured ‘THD vs Frequency’ performance for each DAC, as a way of advertising it!
Finally, from amirm graphs one can realize that what it is considered to be the default, at least stated as such, PCM filter used for both DACs measurements is “F-3: Linear Phase Fast Roll-off”.
Maybe
@amirm could clarify this!