I suspect the paintings to a degree show sloppy baggy sails for artistic drama. I can't see that rig being any different from any square rigged ship other than lateens aft and often no jibs in the art, though one drawing shows a sprit-sail, so I'd guess jibs would be there in reality.

I can't imagine it wouldn't actually be a stable docile thing with all that beam for the length, sails properly metered, set, and taut sheets...

Not seeing the problem you see, but I'm not really a sheet-ship guy, though I find the engineering fascinating. Grin!