We've know that vampires are flammable since Twilight. This issue doesn't seem like a discrepancy to me. Just a new perspective. I agree that before BT burning the pieces seemed like a way to make the vamps seem even more indistructable. That even their pieces needed to be buned.
However, this is the first time we've seen through the eyes of Human blood drinking vampires. They have opened a new world of vicious possibilities. I still think Victoria licked Diego's fingers one by one to coat them in venom and then burned them. This was only possible because she ripped off his legs first and had Riley hold him down.
Also if you think back to the nomads from Twilight they approached the Cullen's in the baseball field very respectably. This implies that they had fear of a Superior group and what they might be able to do to them. Again showing that even in Twilight vampires had weaknesses.
I also don't think this vulnerability makes vampires like a new version of humans. There is one big difference. Everything on this Earth will die. If you believe in souls then you believe that we are eternal and Christian's believe we will be given new perfect bodies in the afterlife. However, this first earthly body will perish.
Vampires have the ability, if uninterfered with, to keep their bodies forever. To never die. They may be killed by other vamps or wolves but they also might not. That is a big difference from humans and not more of the same.
Potentially a vampire with Fred's ability could live until the Sun goes nova and maybe longer if we find out how to live beyond our solar system.