I was gonna say the same thing since I also just copy-paste URL which works fine, but I was never able to find a way to remove shorts. I just tried OP’s instructions for that, I am so happy to finally have no shorts in my feed!
I’m actually surprised that YT is not forcing the shorts on everybody (yet).
I would hate being constantly pinged by those but hey, most of the channels I’m subbed don’t rely grind the algorithm and just opted out from that. 
You can similarly obtain the feed for playlists like so:
- Copy the playlist link with the share button. It should look like:
https://youtube.com/playlist?list=[]
- Take the string after
list=and place it afterplaylist_id=in the format below:
https://www.youtube.com/feeds/videos.xml?playlist_id=[]
This simple site can do it for you: Youtube RSS Extractor by jeffkeeling