Okay, so I did end up finding a solution (immediately after posting). If you go through Piped, they added an option to filter for "shorts" or "videos".
For example, this is the link for Steve Mould without the shorts. Just slap &filter=videos
at the end: https://pipedapi.kavin.rocks/feed/unauthenticated/rss?channels=UCEIwxahdLz7bap-VDs9h35A&filter=videos
Not sure if I want to use Piped yet, although I guess the less you interact with actual "youtube", the better.