DS II does make sense from an in-universe standpoint, it’s just incredibly lazy out-of-universe.
Absolutely. At least it makes sense within universe unlike Starkiller Base.
Here’s a rundown on the similarities between Duel of the Fates and The Rise of Skywalker.
https://screenrant.com/star-wars-9-rise-skywalker-duel-fates-script-story-similarities/