M.Attack: Gildarts <<< Natsu (Natsu's spells are too strong while Gildarts dont use any magic spells)
Ph.Attack: Gildarts >>> Natsu (Nothing to say, in Ph. Natsu is far below him)
Defense: Gildarts >>> Natsu (Gildarts survive from Acno, Natsu has not much def, he has high stamina (main character stamina))
Stamina: Gildarts ? Natsu (Natsu is MC, his stamina is too high but after all it is Gildarts, he cant not have stamina (dont know how write it correct)
Speed: Gildarts << Natsu
Versatility: Gildarts >>> Natsu
Intelligence: Gildarts >>> Natsu (Natsu is stupid. It is all)
MP: Gildarts >>> Natsu (Nothing to say, Gildarts MP is on a different level)
Gildarts >> Natsu
Gildarts will win.
Difficult - 4\10
I've got to disagree here with you.
In general when it comes to attack, Natsu >> Gildarts. Gildarts best feat is launching Bluenote with one of his best spells, meanwhile Natsu has taken the same guy out eight years later with a simple roar. Its clear from this that Natsu is much stronger than Gildarts in attack. Natsu has also launched Bakel (someone who looks bulkier than Bluenote and could well be heavier) with a punch so I'd say Natsu is clearly stronger than Gildarts.
Surviving Acnologia isn't that great a feat when you consider than Acno was playing around with Gildarts, unlike when he attacked God Serena. If Acno was serious, Gildarts wouldn't of made it back to the guild.
Natsu has better feats in Stamina, Speed and Versatility (Lightning and Flames > Physical attacks and light attribute). Intelligence wise, Gildarts hasn't shown himself to be an incredible in tactics anyway, so I'd say they're pretty much matched there.
MP wise, I'd say Gildarts would be only just by a little bit but at this point it wouldn't be too big a gap with the Spriggans having an even bigger MP shown from what we've seen.
From this, I'd have to say its incredibly difficult for Gildarts to win, and Natsu has the attack power to drop Gildarts pretty easily from what we've seen.