User blog comment:FairyRaven/Fairy Tail Chapter 423: Do It All for Love, Review and Commentary/@comment-46.176.172.254-20150315103541/@comment-1359322-20150315105937

Considering how with three months of training, Mira, Elfman, Gajeel etc managed to catch up with mages 7 years later, i don't find it ridiculous at all.

At least for that 1 year, while Lucy and the others have to work in order to live, Natsu has the luxury of not working and fully focusing on his training. He did train in the mountains, he can just hunt for food and sleep outdoors. So time wise, Natsu should be considerably more powerful than he was 1 year ago. He even had the second origin unlocked by Ultear, which according to her, should help Natsu improve even more than usual.

Long story short, no point thinking about power scale. Your talking about a show which has Natsu being 1 shotted by Laxus, Erza etc. Yet still capable of beating opponents of their class.