And if it was really Anakin then I guess it was really Rex and all those poor clones who had to die all over again just to teach Ahsoka a lesson!
In all seriousness if anyone wants to believe that it was the real Anakin then go ahead. You've got "I've been told that before" to lean on and the warm fuzzies that believing it was really him brings. You could also make the argument that Ahsoka's "Anakin..." when she's pulled out of the water suggests that she even believed it was him.
But for me personally it's much more logical to assume that this Anakin is just as real as the one Luke encountered on Dagobah, complete with parallels of the test ending when the decision to decapitate or not decapitate him is made.
I think the emotional impact of Ahsoka's journey remains whether it's him or not, and that you can even still have it somewhat both ways in assuming that since Anakin is now "one with the Force" that his consciousness could have had a hand in guiding the vision that Ahsoka was experiencing even to the point of adding those little flourishes like his specific mannerisms and reference to a duel that she never witnessed. Either way I suspect that Filoni will blab all the details and settle the matter just like when he finally shared the mind-blowing truth that if Qui-Gon hadn't died things...would have been different, lol.