I have used spades for years in my coarse match fishing, and using a hook tyer becomes second nature. I am not convinced using heavy mono for a sea hook would tie as neatly using a spade end whipping type knot. Most knots seem to use less turns when heavier line is involved. I would want the security of at least 6-8 turns on a spade end hook, so think that would be troublesome to tie using, say, 30lb line.
I have tied eyed hooks using a whipping knot though, i.e. use the eye as the spade, which does give a neat knot. In coarse angling most anglers switch over to eyed patters when you go up beyond about a size 10 or 12 hook. I guess the wire gauge is then sufficient to provide enough strength to a knot threaded through the eye, rather than secured up against a spade.
Also, remember, that spade end hooks are generally small and aimed at using tiny delicate baits. If you thread a worm or fish bait up over the eye of your sea hook the streamlined benefit of a spade and whipped knot is lost.
In answer to Trampster's point about hook technology, the hooks that predated spades were actually just straight shanks and were whipped on and varnished to ensure the knot was secure.