I remember being amazed by how great swiping was, and after using it recently (it's not really great on gboard or samsung keyboard either, not bad but just meh) I was wondering if it was just rose tinted glass. But nope, I booted up my old nexus 5 with a normal gboard (not even swiftkey!) and it was still amazing. The contrast was amazing even when I wiped typing data on both phones to make sure that it was a fair comparison.

I guess the most glaring difference was the subtle, but extremely important handling of edge cases or particularly ambigious letter combinations. Even the "bad" modern google keyboard is still 95% accurate, but the difference between that and the 99% accuracy on my nexus 5 basically makes all the difference. It goes from predictive magic to having to swipe across every single letter to make sure it works.