Paintings?

[Seraphor]

Having just done the EW vistas myself, yes you need to discover every single vista in a 'set', and each expansion is it's own set.
This of course requires completing the jump puzzle of each expansion, so if you want ANY paintings from Stormblood zones, you need to get to the top of Kugane, jump off, and land on that lamp post.
Luckily the Radz-At-Han one isn't so bad.

Or you can buy them off the marketboard. The strange thing is though, if you search for 'Paintings' it only displays the first 100 results with no options to change page, so you'll only have paintings from ARR and a bit of HW on there. You'll need to search for individual painting titles to find anything after that.
There aren't too many available though because not many people unlock and/or sell them, and those that are tend to be listed for wild prices of anything between 10k and 100k.