They have 3 whole months to train, they'll be back to OP and hax soon enough. The fights might be good in the tournament but imo FT will win unless some dark guild attacks them during the games
and something epic happens, but otherwise FT will win, no doubt about it. It would be lame,if Fairy Tail becomes again the number 1 guild in just one arc. Also,3 months seems a little time for
getting stronger to me...And Rogue with Sting don't seem like some lame opponents. Natsu couldn't defeat with ease Max,what makes you think that he will defeat those 2?
Remember Natsu is not the only one participating. We also have Erza, Gray, Juvia, Freed, Gajeel, Wendy, Mirajane who is also s class and very powerful and finally we have Laxus who is a beast. All of these characters would most likely become much more powerful and as a result I can see them actually winning. 7 years ago Fairy Tail were the best and even though other guilds caught up and surpassed them, Fairy Tail can still reach the top and honestly they are probably still the strongest guild because I doubt anyone is close to Gildarts level. It would not be weird if they become the strongest. I just hope the author doesn't make Natsu the hero again with him finishing off the most powerful opponent.
I actually think that there's a possibility of FT losing in the tournament, simply because all the previous arcs had life threatening situations. Most or all of them had FT fighting against mages who were a threat against FT members, innocent people, or the world itself. This time it's actually a tournament where nothing negative happens in the end, so there's no real reason for FT to actually win. I personally hope that FT loses, just to show that they aren't as strong compared to the current generation.