Psvita could have been succesfull if it had at least the same support as PSP but it had a lot worst support from 3rd party.
People who said it's because of Sony first party lack of support i tell them that no matter how is the first paty support without third party support you can't succeed
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m