Well, the past arc puts the power we have seen from gildarts so far somewhere between "worthless fodder" and "adequate secondary character" depending on plot requirements. I mean, just look at what his power compares to nowadays. His former peers in terms of power either got a dramatically huge increase in terms of power (laxus) or simply got outright foderized (jura). And the guy that foderized jura was in turn foderized as well. And the guys above jura in the wizard saints also got foderized. And half of fairy tail seems to be well above what gildarts used to have. Erza, natsu and grey seem to be dramatically stronger. Lucy has suggested that while she won't beat natsu she can hold her own. Which means that conservatively lucy can hold her own against gildarts, as we have seen him, and stretching it a bit he could even beat him (he did pretty well against ajir and is literally the sole reason jacob was defeated). Her worst case scenario would be the stellar spirit king which matched mard geer with the power she had one year ago... A stellar spirit king today could probably take on a springan. Screw it, even dragon force wendy would be able to do something here. a year back wendy was a match for second origin jubia which puts her base form well above natsu before the GMGs. Add in a presumably large increase in power and then dragon force and you have a force to be feared. Anyways, back to the point. If gildart, as we last saw him, is so vastly outclass by so many mages and is so far away from being the strongest or even in the same tier as the stronger mages around, then there being god knows how many missions he can't complete is pretty much a certainty. It's a big world and the people we used to think were top dogs are far from that.
For starters, Wendy couldn't stand under Bluenote's Gravity. How can she possibly best Gildarts?
Half the guild? That's a pretty outrageous exaggeration. There's a case for Natsu and Laxus, but how exactly are the others above Gildarts (as of the silent chapter)? You do recall Gildarts was still strong enough to toy around with Natsu and send him flying and then scare Natsu shitless after showing a serious attack. And then Gildarts has crash and disassembly which works on both magic and people. That's seriously underestimating Gildarts tbh.
Yes Gildarts took a larger chunk, but it's just a lesser deadly chunk. A head is smaller than an arm or leg, but it's no more difficult for Acnologia to take. But I'm not really getting at Gildarts durability. It's quite obvious it's a non-factor here, Acnologia can breach it easily. I mean we're talking about a guy who can kill Igneel, yet Gildarts survived.
I think if we're going on the fact that no one survived beforehand, then luck is a realistic possibility.
That's comparing Gildarts durability to Acnologia's offensive power. Obviously the latter far outclasses. But Gildarts durability compared to Serena's is a reasonable one. That's my point. Also, if Acnologia had to use another attack (or with more seriousness) than the first, that's still a plus for Gildarts. Acnologia ripped Igneel but he did that after they had duked it out a fair bit.
About it being less deadly, that's only speculation. It's just like when Jura hit Orga and Laxus in GMG. Orga went down, Laxus got back up. Jura used a minor attack in both cases. That's pretty much how I see Acnologia and Serena/Gildarts. Acnologia used an attack on both (not going all out), one survived, the other didn't. Tbh, I don't see why one can't attribute this in part to Gildarts resiliency.
Not really. It can be said that with the level of attack Acnologia uses normally, people don't survive but Gildarts could. Anyway, I guess there can't be a compromise in this