The weakness with all mechanical leverage systems is the metal/wood joint. Doomed to fail sooner or later.
Making the whole thing in carbon fibre might work but what to do with all those awkward looking bits when sailing?
I'm happy to row “Four Sisters”, my CBL, in the conventional way (......easy to make 3 knots for hours on end , now I have oars the right length!) using a rear view mirror fixed to the mizzen mast with a bit of shock cord, as and when required. Not brilliant but good enough. I can't look over my shoulder as the cabin is in the way – something to be grateful for when rowing into the wind! For more precision when docking I stand up to row, facing forward. You can do that with longer oars. They won't fit the cabin but, anyway, I always keep them in the crutches, ready to use, with the blades fixed to the gunnels with quick release knots. Very handy! (Also, if I miss stays in a light wind – been known to happen! - a quick swipe with one oar brings her round before anyone notices!)