I added the Flirc Kodi remote profile to my Harmony remote and repeat rate was the same.
I adjusted the interkey delay on my Harmony remote between 100 and 1000 and the repeat rate did not change.
The interkey delay option on the gen 1 seems to be the only way to adjust the repeat rate when scrolling in Kodi using up/down or page up/down. I did notice that changing the interkey delay on my Harmony remote had a little affect on the gen 1 repeat rate, didn't test this at multiple values like I did with the gen 2 though.
If there isn't a way to adjust this on the gen 2 I'll be returning it as there are zero pluses currently and one big negative with the gen 2.