There's really no comparison. The PW1 was, err, not great, to put it mildly.
Barring lab126 niceties (the most user-visible one being proper nightmode handling), Mk. 7 devices (meaning the Clara/Forma, mainly), as far as how the screen is handled, have finally noticeably caught up with Amazon, and no longer feel like you're holding a previous generation Kindle, but worst.
In your specific dictionary use-case, you're more likely to be bothered by the fact that the English dictionary is just not that great compared to the Kindle's than by how the UI is handling it
. (Fortunately, provided you're in WiFi range, there's a Google/Wikipedia lookup right next to the dictionary. I'd still much prefer a decent built-in dictionary, but, still
).