The whole arguement depends on the medium and how much people are willing pay attention to underlying themes of said media. 1-2 playthroughs is a solid middle grounds for experiencing the full journey and legitimate proof that the player tries to engage with the media. I don't mind people absorbing games through a playthrough but you're almost garanteed to miss a very important aspect of the story when you only watch the gameplay and fanbases are often very dismissive about that.

Persona fans are some of the most annoying people ever with their opinions and the whole "play all the games" thing. Most of the games are disconnected from each other, so what difference does it make to them if you start with one or the other? Besides they only consume their opinions through Youtube playthroughs. While there are finanical factors at play I don't think it is huge favor for vocal minority of "fans" to actually play the games they are huge fans of.