It *is* technically less neurotoxic than MDMA according to one study, done on rats. So, that doesn't say much. Regardless, it very well could be less neurotoxic than MDMA, but that doesn't mean it's less harmful in a multitude of other ways. Also, I think it's hard to compare which is more or less harmful because it depends on your use of either, how much, how long you use, etc. I've never done MDPV or Mephedrone but from what I've heard from others who have, you're more likely to redose more often than you would on MDMA, and people on bath salts tend to be up for days, not just a night like most people who use MDMA are. So, sleep deprivation itself, will obviously cause a whole slue of other ill effects on your brain and body. And... as far as I know, although they're kind of similar chemicals, MDPV/mephedrone work primarily on dopamine/norepinephrine, where as MDMA works primarily on serotonin, so it's hard to say. I think the "scary" or most worrisome thing about bath salts is more so the sleep deprivation that typically comes with doing it, not even the actual drug itself. It seems like people go into psychosis on it easier. I can only speak from what I've researched and heard from others though. A friend of mine who did it was awake for 3 days and said the others who had done it with him were definitely flailing and going a little batty much quicker and easier than he's even seen on meth. So, even though it's possible that MDMA is technically more neurotoxic, over all, whether or not it's more or less harmful than something like MDPV would depend on your use.
As for whether or not what you took was MDPV/mephedrone, I've never done it, so I couldn't tell you, but I do know that if the euphoria is short lasting and it doesn't taste very bitter, it's either not MDMA or doesn't have much MDMA in it at all. MDMA is sooooo bitter...