Well, maybe it’s a matter of personal opinion. The word disgusting is a word I would use to describe the taste of something that’s gone bad…or someone that urinates in a small swimming pool… or… well…
This problem you are describing is something I would call inconvenient. It’s not very user friendly… it might even annoy the sh*t out of you. I understand that.
I have 2 monitors and I use littlenavmap and charts on my second monitor too.
When I go to my second monitor to zoom in on the littlenavmap MSFS zooms too, unless I click first to make that window active.
To me, that’s logical. I don’t want to look up some airport in LittleNavMap and discover that I have turned the autopilot off in MSFS because I pressed the Z key
When I go back to MSFS I do the same. I click that window to make it active. Also ALT+TAB works.
So, yes… maybe a little bit inconvenient… but Disgusting? No. I respectfully disagree on that word.