I've had more experience with my Garmin Striker 7sv, most recently on a small trout lake with a fairly hard clean bottom and depths to 36' with sparse weeds only in water 2' or less. It did well under those conditions, since there was little on the bottom, structure stood out well.
The screen is somewhat small at 7" so using left or right side only views (when possible) rather than both-side view helped. The targets were mostly small. I was able to make out an occasional sunken tree, and rocks of, say bowling ball size. Even individual fish (I think) as small bright pinpoints.
All of this was with the settings I've listed earlier in this thread, 455kHz and Amber hue were absolutely essential, and 40% contrast, and auto-med or auto-high for brightness were helpful.
I caught 3 rainbows, and lost or released a half dozen others, and I believe the SI did help me get in the vicinity of where fish were holding under these conditions. Of course in conjunction with the normal down imaging. In the down imaging, which was excellent, I was able to see my vertical jigging lure if the boat wasn't drifting, and could control depth, and I even saw a couple of rises to it and takes.
I'm still looking forward to trying the SI out on crappie habitat elsewhere.
So through all of this have you confirmed your transducer is level front to back and side to side with how your boat sits at sonar speed? It will not be level with the hull of the boat, never seen one that was. You do this by using a level on the side and center deck of your boat while you are moving at the correct speed. Search on youtube "leveling side imaging transducer" and you will see the tricks on how to do it.
For side imaging you want to be at 3-5mph, any slower and your images will look fuzzy like in your pictures. Keep your speed at auto.
Garmin 800khz side imaging is phenomenal, your pictures definitely say something is wrong. way more than 9 out of 10 "my side imaging looks bad" posts are due to incorrect installation of the transducer. Did we see any pics on how its mounted to the boat?? I read most replies and didnt catch it.
Buddys of mine have the same unit and you can pick out a crappie sitting on brush 40 feet to the side with ease, looks nothing like your pics. Your pics look like my old humminbird. My garmin UHD side imaging is like looking at a picture, I can see 12" sticks laying on bottom off to the side and count the number of fish sitting in a brush pile.