So, there you have it OP, there are several ways to skin cat.
What would I do now? I think I'd ask Google maps for their route A to B (port to Baden Baden) which would give me the distance and direction. I would then ask it for A to C via B (port to Baden Baden to destination in Switzerland).
I'd then sit down with my mate to work out whether I / we wanted to go to Switzerland at all, not least as you don't seem to be particularly sold on the idea and / or might be happy - if you found something fun on the way - to not end up going or reduce your time in the land of Toblerone.
Then I'd look at Google map's blue line A to B or A to C via B, to see what lay either side of it that would, whilst keeping the same general direction, offer some good fun. I'd then consider that, if I mucked about in say the Ardennes for a full day or two (ie getting no closer to Switzerland, which was the original purpose of my holiday) I could also make most of the time up by hitting a motorway or getting up earlier, cracking on and not stopping to press wild flowers.
I'd also probably think to myself, I was going to go, A to B (port to Baden Baden) in one hit, so I chose Baden Baden as the furthest point I could imagine in order to hit the Black Forest the next day. I'd now realise that if I instead went port, to Ardennes and had a full day and two nights there, I could go deeper into the Black Forest the next day, taking myself right into the middle. From that central spot, I couid then have the next day hooning in the region in just about any direction I liked. If I liked it so much I could stay and / or make up the lost day on a motorway and still make it to the far side of Switzerland (if necessary) or give up on Switzerland completely. If I did that, I'd consider going into the Vosges and then up into the Morvan before going back to the port by any route that best suited my definite need to get on a ferry that would not wait for me.
What I wanted to see, I'd decide, as only I knew really. What I'd think would be fun to do, I'd decide too, for exactly the same reason. If I really did not want to touch a motorway, I'd ignore any advice or option that told me to. In short, I'd wing it or plan it or both... but, whatever, I'd do it my way.