As a owner of the 2017 and 2018 for me the 2 big advantages areAs an private owner of a 2017 and a company issued 2020, I can point at several advantages for both and numerous ties. The single most important advantage of 2020 is the pencil and how it charges. The rest is not obvious to me. Performance is sufficient for both, finger print button is easier (no bring your face closer), the 2017 is easier to hold because the bezels are larger, the 2020 is sleeker because it lacks bezels, cameras is better on the 2020 but I have an iPhone. Not a single feature in 2020 is a deal breaker.
1. USB C (huge since my phone is USB C, so can charge with the same cable and can use external storage without power or even adapter, which is a big deal when you don't have airdrop and need to move large files from phone to iPad)
2. pencil 2 (just like you said)
Other smaller but still relatively significant advantages for me are Bluetooth 5 (much more range with airpods around the house) and Magic keyboard support (better than the logitech one I got for my 10.5) and more screen for roughly the same size.
And last but not least, no white spot on the 11 pro (I know not everyone has one...)
Other than that, performance on the 10.5 is still sufficient, I don't care about cameras, touch id is better than face id for me too (I kind of hate face id, wish it was like Windows hello, but it isn't...)