He didn't gain or upgraded anything, it is not a sudden power up unless you can prove it, at least with one year training, that where he most likely got it, not something out of no where.
Jacob was just about to send them back to Transport but Happy or in his way, and then makarov punched him, not grabbed him. Plus with the pressures he was hit with is logica for him not to concentrate for either stealth or transport.
A one shot is when the fight ends in the first hit or attempt, since it did not kill Wahl first hit, it can't be a one shot.
Jacob couldn't focus when he was in mid air and when Natsu was coming in like a wrecking ball.
When was that considered an upgrade when he was training for a year, that was the fruit of his labor, it wasn't a one shot either since Laxus had been attacking him relentlessly.
Jacob couldn't attack when he was in mid air being pushed back.
Well Laxus had learned of his great grandfather during the GMG, this not only provided plenty of time for him to study him but train to gain the same power as him.
With Makariv punching Jacob through the guild is not that impressive, though strategically, it gave Natsu to edge to attack Jacob while he can't focus on his stealth or transport.
S'no problem. I had to laugh when I saw it.