I'd say that its largely too late, but that doesn't mean the remaining couple of arcs of Post-ts can't be just as good or maybe even better. It's just unfortunate that the majority of Post-ts would be relatively subpar even if the ending is spectacular.
You can basically define "better" in a number of ways in this scenario. If we are talking about consistency of quality then it is definitely too late. If we are talking about comparing the peaks of each section then it is still possible.
Then again, I'd like to think that the current arc is mostly suffering from Oda not really knowing how to handle the current antagonists well, and that the stuff coming after this is just more relevant and interesting that it will be impossible for him to fail to deliver. Maybe that's just wishful thinking, but looking back at the entire series I'd say that Oda consistently nails it when the main plotline involving the World Government is involved.
All that aside, I can think of very little that Post-ts does better than Pre-ts. I think chalking it up to nostalgia is just a poor excuse since I'm one of those that followed it in one go up to Dressrosa, and have both rewatched and reread it since then.
Pre-ts is not without problems, but Post-ts exacerbates them which is not good. It is also unavoidable, but the first time encountering a problem will obviously not be as bad as the 5th, 6th or umpteenth time. So saying a problem was in Pre-ts too is not really a good excuse.