User blog comment:IamJakuhoRaikoben/Chapter 394: Juvia vs. Keith, Review./@comment-24800928-20140725181935/@comment-24066070-20140726013132

About Gray acquiring the powers too easily, he had already proven his compatibility and here we have a father passing magic to his son, which is more or less similar to the first gen DS learning magic from their respective parent.

I think the second gen DS acquired their power in a cheap way. They just implanted a lacrima and that's that. No need for them to prove their compatibility at all, heck those lacrima may even work on anybody.