User blog comment:R. Lawton/How strong are some the GMG characters in comparison to Fairy Tail/@comment-7418318-20130911001131

There is one problem and that is "It's a story"

If Mashima would have gone by logic alone, FT would have simply brushed aside any competition. But that wouldn't have been interresting, so he needed to make the other competitors roughly equal in power to the Fairy Tail mages, which naturally puts them above the tenroujima strength of the FT members.

It's a tradeoff that was necessary to keep the story interresting, the same way as games make trade-offs to the backstory for playability (like game X-Wings not blowing up from a single hit like in the movies).

And there's also what Rai said already. Would you have liked to see only people several years older than the Fairy Tail members as their enemies, just so that it fits in logically, in a series that never relied much on logic in the first place?