Obviously a misunderstanding on both sides. I plot a route on CT, transfer it and navigate in Osmand on the phone. The same route is also keep on the tablet. If I then wish to change the route I do that on the tablet and transfer the amended route to the phone. I don't need any internet connection to do this. The advantage of the tablet, just like a paper map, is that I get a wider area to view and a greater understanding of where I am. Unlike a paper map I can find the nearest corner shop marked in osmand. On the tablet I don't have to peer at a small screen to find the nearest corner shop. In the evening I can look at the planned route for next day and alter it to go see a castle or something. If I want an offroute campsite it's a lot easier to use Archie's on a larger screen. All possible on a phone screen but I find that by zooming out to find what I want I can't see my existing route.
Plus I get the advantages of a screen I can read a kindle book, guidebook, etc.
It's just a different way of doing the same thing.
sounds like you're sorted to me climo.
A good use of tech.
I have seen handlebar holders for 7 inch tabs but I don't think I'd have the room, and in any case, on the bike, it's really only the turns you need.
I use a garmin on the bars but may in time experiment with an old/dispensable android phone fed from a powerbank.