I can kind of appreciate the fact that that BETA simply use mixed-unit tactics to completely trample humanity. The Destroyers absolutely tear through front line, but as a trade off for that durability, are weak from behind. Yet they in turn are covered by mid-rear forces, the Lasers. Leaping over Destroyers to get at the Lasers would be effective, if not for the third type, which are moderately strong attackers with good mobility.

This is pretty much the way a real alien invasion would go down. If they're advanced enough to cross star systems to get to Earth, they're advanced enough to crush humanity completely. The BETA have overwhelming numbers on their side too. We can't even leave the Solar System, and there are so few stories out there were a race advanced enough to do so doesn't also have the means to dominate Earth.

Still, how or why they're so strong doesn't particularly matter. All that matters is that they push humanity to the brink.

Watching this episode, I also wouldn't say it's a matter of the girls fighting better than the veterans. Everyone sucks against the BETA. Our viewpoint is just focused on them longer. Yui loses a comrade every couple minutes, and that's not even in real time given the cutaways to her uncle, the regular forces, or whoever. The majority of the time where they're surviving, they're retreating at full speed.