I agree on every point except that Soresu is at a disadvantage against Djem So (and the fact that Obi-wan being overwhelmed makes the point moot. Prior to that point he had disarmed two of Grievous' sabers using purely lightsaber combat, something no other jedi had done). In every other instance (even in real life) where power is used against redirection, it's power that gets the short end of the stick. Again, Jiu Jitsu vs wrestling is the perfect example. Wrestlers are trained to use power and ferocity to dominate their opponent, where Jiu Jitsu practitioners are trained to use their opponent's own body, power, and ferocity against them. 9 times out of 10, given equal levels of skill and appropriate conditioning, Jiu Jitsu will win simply because it no longer matters how powerful or ferocious the wrestler is. 

The primary difference between Soresu and Shien is that Soresu waits for an opening while letting the opponent wear themselves down, and Shien works to create an opening to exploit. Djem So, on the other hand, is not even remotely as reserved as either Soresu or Shien (which should really be its own style). Sure, Soresu on its own won't beat any other style, but only because it has no offensive moves. The thing is, that doesn't matter because every jedi learns form 1 before they can move on to another, which gives them the offensive options to utilize once their opponent gives them an opening. No duelist uses strictly a single style. Every time a Djem So user deflects blaster bolts, that's Soresu. Every time a Makashi user vaults over their opponent, that's Ataru. The point I'm making is that a Soresu specialist has an advantage over a Djem So specialist because they can outlast them every time, then utilize the offensive measures learned from form 1 to finish the job. The powerful swings Djem So requires are unequivocally more tiring than the subtle dodges and parry's of Soresu.

All that said, I need some help deciding if I should use a force user or a mercenary. :P