There's no need to camp. Skywatcher npcs in the main cities can tell you the next few weathers for each zone and the weather changes always happen at 12:00 am, 8:00 am, and 4:00 pm Eorzea time.

As for why the later ones were made easier I guess the devs were responding to complaints that the ARR ones were too annoying.

The paintings are tradable so you can try asking in Shout or a server only PF if anyone can grab the ones you want. I've got my log done and get paintings for players that ask for them in the Novice Network sometimes.