Well, after letting steam out, I think I was not completely honest. Hardware on this player is very good (not CPU though, audio), it has a lot of BT codecs, can DAC sound into USB socket, so if someone would adapt LineageOS or even make some custom firmware (there is one on xda). Potentially I could tether player to computer, install AntennaPod on it and have music and podcasts on one device, thus I could leave my phone home on hikes.
Fun part that I already (probably, can't remember) tried to do something, because when I went to unlock developer's menu and on stage when you have to click 7 times on kernel version big brother gently tapped me on shoulder and said something like "no need, brother, you already granted permission to install whatever".
Basically, Android is such overkill for that player, so much useless stuff for a music player, I wonder when it gonna get out of style to solve programming issues with throwing in more CPU powers instead of working on optimizing code.
Anyway, rant is over, now I'm thinking on reorganizing apps or even maybe build custom android with throwing away half of code, I don't need security features, all I want is be able to run one! single! app for playing music and it be able to read SD card
Holy shit, with Auxio instead of FiiO Music I can stand this device again! Opensource saves the day! Again!
Rejoice! Praise FOSS!