After having bad luck several times myself, I finally got an assym to work for me, but it was a very mild assymetry.
I had a zone classic drilled with the m.b. strong, and it would roll out and stop hooking at 35 ft. I tried a friends total annihilation with the m.b. strong and it had much the same thing going on with it. I swore off of asymm's.
Then, I got the chance to throw the blue/green centaur. Granted, it is a weak assym, but it was also drilled with the m.b. in a weak position ( left side of thumbhole ) and it worked great.
I then got an Impulse zone. Not quite as strong as the classic ( the assymstry at least ), and I drilled it with the m.b. at 90 degrees, way down past the v.a.l. This ball was also very smooth and usable.
So, I finally decided, it was probably a bit of both of the factors you mention because, with the m.b. strong, I couldn't use an assym either, but with the m.b. in a very weak position, I got a good reaction I could use.
Assym's don't work well for everyone, but with the proper drilling, they can be used. It's just hard to find the drill that is right for you sometimes.
Remember, assymetry is used to enhance the balls ability to find its preffered spin/roll axis. If you have a hand release that already spins/rolls up quickly, the added strength of a m.b. may only cause the ball to spin up/roll out sooner than you would want. Usefull on total floods, but hard to gauge on a THS.
P.S. I prefer symmetric cores, but after much effort, found a way to drill an assym that works for me. But, even after I did, it didn't work any better than the strong symmetric balls I already had. Only the weak drills allowed me to use them at all. I cannot envision EVER finding enough oil to use an Epic Battle ( or something similar ) with a strong assym drilling.
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"TOO SOON THE POWER, TOO LATE THE WISDOM"