The regular military was having a decent effect on Alucard's main body, but unfortunately for them, that was also when Miyabi/Alucard decided to rejoin with the main body because it was underperforming.

Regarding San, it's important to note that everyone at the Academy during the years she attended is terrified of her. She's one of the strongest students in the 100+ year history of the Academy. There is a very good chance that her opponents have already lost before they even notice she's there, as her attack melody is well above the hearing range of...just about anyone, including other Sirens. Most vampires don't even stand a chance against her. Shinso are probably the only ones who can survive for more than a few minutes due to their insane regeneration.

All that accumulating damage (which it turn forces the Shinso to focus healing her distributed damage) helps others do substantially more.