Pretty sure you're right.

Alliance can get to Galv before horde can get to Belinda.
Either can get to their own Captain before the other can get to the opposing Captain.

If twenty alliance attack Galv, and ten horde are inside, the alliance die 95% of the time.
If twenty horde attack Belinda, ten alliance (myself and five others) were not enough to survive always.

Galv is a lot tougher.

Not sure why, but at 60th and 70th, my AV record was 95% (as alliance).
While at 80th and 85th, it is closer to 20% (also as alliance).
On the same server, etc.