Re: aikido vs jiu-jitsu
"Brazillian Jujitsu" is founded on the original Kodokan Judo Newaza syllabus. This syllabus was developed to be used in conjunction with the full range of Jujitsu waza (hand /foot strikes, throws, joint locks, strangles) that were amalgamated to form Judo.
Any defense/offense system that specializes begins to omit training in situations that don't fall within the operational range of the specialty. If you want to learn to fight, Uke must attack with skill, using jabs, kicks, slaps and combinations there of. Any defense that presuposes a one event, overextended strike, kick or grab, and doesn't presupose a "plus one" opponent and an edged weapon is incomplete if your goal is to learn to fight a fighter.
The next time you are uke, try poking a finger into Nage's ribs as the technique is being done and you'll see how quickly ki is distrubed and ma is broken.