Okay, let me throw this one at people.
Throughout the manga, we've seen Natsu grow and we've also seen that in the last year especially that he did an immense amount of training in that year, and became strong enough to one-shot someone who was just as strong as Gildarts with ease, which is quite impressive.
Jellal on the other hand has never actually shown any signs of any growth whatsoever throughout the eight years since the ToH, so without anything to actually indicate he got stronger its actually pretty clear to me that he's been at the strength to one-shot Neinhart since ToH. Now if you remember that just a thoughtform was enough to have him recognized as powerful enough to become a Wizard Saint and enter the magic council, then it becomes a whole lot more believable that Jellal has always been at this level.
Now if you think back to Natsu at that time who when in Dragon Force defeated Jellal, the most powerful person in the manga at that time, with just a few punches, then it makes Natsu's feat at the time all the more impressive. And, seeing that Natsu is now much stronger while as I've stated above, Jellal has shown no signs of actually growing stronger in anyway whatsoever, then I think its clear that Natsu could actually clean Jellal up even faster than he did back in the ToH arc as he's much stronger, faster etc. now.
But you need to think that the higher he goes the less his accuracy is going to be, and seeing Grand Chariot doesn't have a feat of traveling too far, that'd leave him to drop big Sema's again and again which are very draining on him. And if he is going to do this from really high up like you said, then Natsu could potentially get in a position to avoid the majority of the attack, perhaps even fully avoid it.