Well even though it has been three years, Bloom still is new to the whole magical relm thing. I agree that she is the most powerful fairy, but at the same time she isn't because she lacks confidence and control.
Ever notice that the Dragonfire mostly only ever comes out when Bloom becomes enraged? Because she looses control.
If Bloom were to fully master and control her powers, then yes she would be the strongest, probably in the whole magical relm. But as it is, she is still learning, theres so many questions that she has that nobody can answer for her, and although
technically she is a creature of the magical relm, Bloom is still the Earth girl. Her Earth parents are her 'real' parents, and Earth is her 'real' home.
So by being thrown into the magical relm, well she jumped in or whatever
, Bloom more than likely became overwelmed, then adding on the whole "You have the greatest power in the entire magical relm inside of you" in her first year of fairy college
probably made her think super great things were expected of her. And if she would be able to accomplish such things everyone would be disappointed. That would probably explain her lack in confidence.
So, as she is, Bloom has the potential to become one of the greatest fairies ever, but she is not quite there yet. And she wont be there until she gains confidence.
Also, each girl is strong in their own way. Each can do things that the others cannot, therefore should the situation call for some specific thing to be done that only one of the girls could do, then that girl would be the strongest in said situation...... catch my drift?
blah I ranted again.... >_<