First of all, I think your statement about separate apps @attah, is correct at least 95% of the time.
Since I use a separate app for Youtube on mobile and desktop, I thought I could give a list of reasons:
- My subscriptions, playlists and watch history are stored only locally
- Ease of using Tor network as a proxy
- Being able to use adblocking, sponsorblocking and other extra features without polluting my browser with addons that increase my online fingerprint
- Customising features like skip amount, default formats and resolution, Do Not Disturb mode…
- Less distracting elements in the UI
Note that not all the features are available on mobile.
To make this post fit better into this topic, I’d recommend following @flypig’s work on bringing NewPipe natively to Sailfish, although I’m not sure if it will be compatible with Jolla Store: NewPipe-dev diary