Based on last chapter, I'd change my ranking:
1. Laxus
2. Gildarts
3. Mirajane
4. Mystogan
5. Erza
Since Laxus can solo a Spriggan, I'd say he surpasses Gildarts with no doubt. If Crimson Thunder can defeat Wahl, it can one shot Gildarts as well.
I wouldn't really count Laxus'
Crimson Thunder. It really wasn't his own magic. Last chapter was a complete mess. There is no way Laxus can suddenly attain power from his great grandfather unless we have detailed explanation from it. If he always had it, he should have used it against many opponents in the past including the Tartaros Arc. There is literally only one possible explanation for such a feat, even so, it would be far-fetched. Also, using one of Freed's magic was total nonsense. What is the point of each character having unique magics when Natsu can just spend a year teaching Gray
Fire Dragon-Slayer Magic while Gray teaches Natsu
Ice Devil Slayer Magic. For those who believed Erza won every fight because "She's Erza", they should take a good look at this fight. Perhaps this applies to Laxus too.
Although I never really liked Natsu getting Igneel's power because I want him to show his true character development through other power-ups like Dragon Force, it made a lot more sense than this.
This fight didn't really prove how Laxus would fare against Gildarts let alone a one-shot.