They new hydrualic discs, and prety sure no contamination ( I do test things before set off).You really shouldn't be struggling to hold the brakes, even with rim brakes. Do you have any grip strength issues ? Hydraulic breaks are so light ?
Are your pads contaminated ?
Big difference with MTB brakes TBH - rim brakes are damn right rubbish on steep stuff, no power, grip of death to try and slow down. Hydraulic MTB brakes are designed for one finger operation (I use two).
Link to bike BTW: https://www.cube.eu/en/2021/bikes/road/road-race/attain/cube-attain-sl-greynblack/