I haven't sailed any multihull boats, but several small dinghys such as Optimist, Mirror, Lazor and a "mini 12" (called 2.4 nowdays?). To me, a boat under sail that leans hard and requires some attention is a normal thing, nothing to be worried about. It's part of the fun...
Yes, but in a single kayak you can't "hike out" to counter-balance the leeward tilt. You can try and lean somewhat, in your seat, but this is both uncomfortable and not very efficient. In a bigger boat like AEII or GII it is possible to use a "hiking board", but then, a bigger boat is a pain to paddle when wind dies. KeyMeKoe has a GII, I think.
And a kayak without sail is capable of covering huge distances, if the kayaker is fit enough. So a sailing rig is optional and not a must for long-distance touring.
sail rig, and especially one with outriggers, is not a must for long trips. It is easier to maintain tight schedule without having to rely on wind. Upwind sail rig with outriggers will
eventually save efforts in long trip, and will make the trip more relaxed, but one can't rely on it if trip schedule is tight (like your return flight is on a certain date or you need to make it back to your car before dark).
Funny thing is that downwind
rig without outriggers will also save about the same amount of efforts - you'll have to paddle more often (downwind rig can't handle side wind), but the paddling will be easier than with outriggers. One major difference is that you won't be able to relax as much as with outriggers. With an upwind
rig without outriggers there is even less relaxing (more fun, more thrill, but less relaxing), and sooner or later such a sailor will flip over. May be not very soon if he is careful, but it will happen eventually
perhaps that [BSD] rig is too complex and static for setting up and removal while underway, even on a very stable SOT or folder with big cockpit
Yes. Mark Balogh (the inventor), of course, claims that it is not too complex for setting up on water, but I disagree with him, and I'm not the only one. Even when stability isn't a problem (like in GII or AEII), there is time and efforts. Those who have BSD know how many parts is there, and all those parts need to be stored under deck when not in use (there is no room to keep this all on deck), and it is a pain to retrieve it from under decks while under way. Putting it on and off takes 20-30 minutes each time, and if wind dies again after you've just put the sail on and you need to take it off again, you feel like an idiot, because all you achieved was a waste of time.