I have to partially disagree. Disregarding the artificial monsters, many monsters show plenty of signs of being female up to Gnome. Granted, some (such as most of the bug-based species) are unlikely to be recognized as female by Luka if the -girl part wasn't added to the monsters by default, it is likely he would've been easily able to identify the gender of most of the monsters, acknowledging that he has been fighting females up to Gnome. The Elves, faeries, and even two of the artificials looked more human than Gnome. Although the faeries would be arguable, since they're so tiny.
However, I suppose it could be related to the younger-looking monsters. There was still a fair amount of those, but most of them were asking for it. It's possible that he felt bad towards the timid Gnome. Even if that were so, a better choice of words would've been nice.
"The power to crush anything slams into Granberia! Luka deals 47210 damage! Granberia falls to her knees!"
Meaning Granberia is stronger than the power to crush anything. I'm going to be extremely annoyed if
her Chimera kills her in part 3.