New hydraulic disc brake has less stopping power than old rim brake—why?
Disc brakes commonly have issues when:


they are not bedded in yet. This is required on new bikes or new pads/disc only. The pads and the disc don't have the optimal contact surface established when out of box; bed-in-process;
they get in contact with lubricating substances. There are many ways to clean them, but mainly alcohol should do it; how-to-clean-disk-brakes;
they contain air mixed in with the brake fluid in the circuit. This is hard to detect and requires a full brake bleed. Generally there are low chances this is the case and even lower that both of your brakes have this issue. Checking if the braking power front-back is close to equal should reveal that. 


If the disc is clean and there is no air in the circuit, there is no loss of power and that is the true power of your brakes. Tektro 160mm is a low end brake so that wouldn't be a surprise. A workaround is to try a bigger disk if the fork/frame allows.