This is where I realized how much info this manga has cut out. As I mentioned above, Rare got extremely lucky. Her getting 300 XP right at the start of the game is already unusual because most beginner players won't spawn in with enemies as powerful as the catgirls (who are counted as bosses) outside their spawn point. Although this is less the problem with the manga, but the novel author did not properly quantify how much XP will be earned if you grind normally, so it was hard to compare just how much 300 XP is for a beginner player.
And to get the subordinate skill, you need to go down 4 different skill trees (3 of those have questionable utility, another thing not explained in the manga), none of those have any offensive skills, and she had to burn through almost 400 XP for it. This wasn't a skill meant for beginner players and most players won't start investing in these skills before any offensive skills, and Rare only did it because she specifically knew about this skill and tried to reverse engineer (or whatever the correct word is) the prerequisite skills. Later on, there is a top ranking player who went down 2 of these trees, but he still skipped over the others because he don't see any point in picking those skills.
With all that said, is this series of coincidences extremely contrived and shows how unbalanced the game balance is? Absolutely and we love this story for it.