Laxus winning is not a stretch or unbelievable. Laxus has grown stronger, it was with his own power. Even if he isn't as strong as Gildartz yet; ergo Gildartz is more than a monster. When Gajeel and Natsu fought Laxus, they both agreed he was a monster especially since he lost a lot of magic using Fairy Law. It is of no surprise that he is stronger now. Jura smiled at the end can mean many things. I still think he was just happy to be fighting someone strong. I don't think he lost on purpose, perhaps fought more close combat than normal, but the fight was shortened so it's difficult to say. It was in all a fist fight.
Anyway if Jura won he would have wiped out the rest of the competition. It is again difficult to gauge how strong everyone is, as Laxus calls Jura a monster, everyone agrees Gildartz is a don, Jellal unsure he could beat Jura even if he tried his hardest.
So at the moment it looks like: (Laxus<=>Jura<=>Jellal)< Gildartz
Anyway Laxus now looks in no shape to win another tough battle, nor will Erza after this, after unlocking her Second Origin, she's gone all out. And out of all the people, Laxus does seem to have the best endurance after seeing him take a powerful hit from Hades with no magic in him.
After reading the previous chapters, I read how a lot of people were commenting how Jura was weak, and now in this chapter they can't believe that Laxus beat him.
Laxus is strong and the only one strong enough to even have the possibility of beating Jura.
Let's review on what would happen if Jura faced the other survivors.
Jura vs Erza/Minerva - Result Jura wins
Jura vs Gray/Juvia - Result Jura wins
Jura vs Gajeel - Jura would probably win unless Gajeel has another power up such as the shadow magic he received, like being Natsu as a Lightning Fire Dragon slayer. However still Jura has the edge in that battle.
Jura vs Sting - (assuming both are uninjured) Jura still has the massive edge of winning depending on Sting's "power-up" in fighting for Lecter.
And Jure vs Laxus - Jura here still has quite an edge, but it is more believable that Laxus has the best chance of beating Jura even if he thinks Jura is a monster after Jura KOs Orga with one hit.
Now considering this is Fairy Tail, if Jura beats Laxus, who else has the possibility of beating him. Though an alternate route could be a final battle between Sting vs Gajeel vs Jura. Where it would be difficult to see who would win. As in this 'theoretic battle' considering the points, whoever beats Jura automatically wins. Or if Jura beat Sting then he would automatically win, if Gajeel beat Sting won considering that Gajeel isn't the captain, then he would also have to beat Jura to win, or a double KO would result in a draw. If Gajeel were beaten by any of the other 2, Sting and Jura would still have to fight to determine the victor.
But enough of that. I will await the next awesome chapter. Mashima will deliver.