I'd be very surprised if the majority of people using an AVR didn't use some kind of EQ, the receiver is pretty insistent on it on initial setup. Hifi is likely a different story.
I'm sure quality control can be an issue at this end of the price bracket, and can foresee a situation where a manufacturer sent item is of perfect performance while someone buying from Amazon may have received a dud.
Interesting stuff. I have the Fosi DAC-Q4 feeding a pair of Presonus E3.5 active speakers in my WFH setup for super non-critical listening and find it to perform similarly to the amp to my subjective tastes, absolutely fine for the £/$ 70 class.