Unfortunately, my main plotter is a Humminbird so can only directly compare my MN Lakemaster chip and my Navionics + chip for Lake Superior waters. Obviously, my opinion of the Lakemaster chip is irrelevant for your HDS, but if you go to the Navionics WebApp webpage, zoom in on Superior/Isle Royale and enable the sonar charts layer, that will be the level of detail you’ll find on the Navionics + card for all of Superior (except the card will be in feet, not meters like the WebApp defaults to).
Actual depth accuracy does seem decrease somewhat the further from shore you get, but the general contours are accurate enough to be useful. I will say that there are a lot of small underwater humps and reefs in the areas that I fish most frequently that are not marked, so I assume this is the case all up and down the shore, but all of the major ones are outlined well enough.
I keep telling myself that I should take a day and record a few sonar logs to upload to Navionics to see if their sonar charts feature is a feasible way to improve on detail/accuracy, but have yet to give that a shot.
If possible, I’d try to run into a Cabelas/Gander/Marine General and see if they’ll pop in the correct Lowrance Insight chip(s) for the parts of Superior you are interested in. At least then you’d have something to compare the Navionics + with. I did that before purchasing my MN Lakemaster chip and much prefer it for western Lake Superior, except for the fact that all data ends somewhere around Silver Bay, so is completely useless to me NE of there.