Hi,
Maybe better than Raspbian?
If you are running on a Raspberry Pi you are still on Raspberry OS 
DietPi is not an own OS, it’s a set of scripts on top of a base image. However the image was reduced down to a minimum. Means, it’s an extrem slim/diet version of Raspberry OS with some magic scripts around.
since some years now I have a Raspbian Stretch running
well you could clone your SD card to gain a full backup. Once done try to upgrade from Stretch to Buster qBittorrent Version shipping with DietPi - #9 by MichaIng
If thinks are failing, just flash you cloned image back