Using LOTS of elbow bend is actually vital at times for effective pumping. The top guys often use heaps of elbow bend, which is one reason they are the top guys.
Check out RSX champ Dorian Van Rijsselberghe at 14 and 30 seconds (very light air) and 2m 18s etc here ;
Mattia Camboni, running second in Tokyo at the moment, can be seen here (
) from 11:24 to 11:32 using heaps of elbow bend. The other top Italian can be seen using heaps of elbow bend at 13:13 while leading the worlds medal race. The big elbow bends occur at times for the next minute or so, at least; I haven't watched the rest.
Mattia seems to use lots of arm bend most of the time as far as I can see, although I'm not normally close enough to really watch after the first lap.

Check out Nico Prien here;
at 1"57 his elbow is so bent that his wrist is almost against his shoulder. See also around 5:18 to see how much arm bend he has.
Personally, I used to cramp really badly but found that moving the boom down as far as I could (allowing for proper sail trim etc) helped. The other things that helped were general cardio fitness (ie bike time), time on the water, and making sure there was enough rehydration.
Good training technique could be a mixture of 30s flat-out efforts and 10 minute threshold efforts, but that's getting fairly serious.
Also check up on tennis elbow prevention exercises.