Interesting find. I’m not able to reproduce that behavior though? If you are using the same full screen approach within SharpTools, it should be the same in either case. Feel free to record a video and share on YouTube / Google Drive / iCloud if you have a specific approach to accomplish what you’re referring to though.
Dashboard vs Kiosk Start URL
Keep in mind that if you start Guided Access while in Safari, you’re basically making the whole browser available, so someone could navigate back and forth and exit out of the fullscreen mode which would make the edit button available.
The same concept applies for the Add to Homescreen approach. As noted in the linked article, most people will want to navigate to the list of dashboards, then tap the ... next to their desired dashboard and tap View (Kiosk) before using the Share > Add to Homescreen option.
This ensures that the shortcut on your homescreen takes you directly into the Dashboard loaded in Kiosk mode so you can’t swipe to navigate back and exit out of kiosk mode.
Kiosk App Alternative
Alternatively, some people prefer using a Kiosk App as it feels more intuitive and explicit for them.