low-end mechanical disc brakes - without better pads and meticulous setup and attention - are barely adequate for rail trails
a change to Spyres or similar would be an mprovement
since the bike is 8 spd - a move to 10 spd hydraulic might be an option ? find a reasonably priced 10 spd hydraulic group of take-off parts - Tiagra 4720 10 speed or similar - from someone selling to upgrade their bike to 11 spd