Future proofing and community funneling

[Jeeqbit]

This is like saying that every limited time event is always accessible

No it's not, because it's still available. It's just that it will be a quieter experience because the community has stopped doing it. Because that is how gamers play games. They login, do new DLC, then leave. Just watch any friend/user list on Steam, Discord. A new game or its DLC releases, they play it for maybe a week, then they move on. Games are just FOMO. SE knows this, and designs the patches accordingly.

Putting aside the obvious fact that I can pick up any old SP game and go through it at my own pace

You can, but it's FOMO in the sense that while you're playing it at your own pace, everyone else probably isn't playing it. Similarly this is the case in FFXIV. If you do Ishgard Restoration 6 years later, probably most others aren't doing it and the "fun" crowd that was there no longer is.

there's still lively activity through older content in many other MMOs via different incentive structures.

There is, but it's specific content, such as a starting open world area. You are talking about making 12 years worth of content and zones still getting bustling with hundreds of players no matter which content you pickup. This just isn't how people play computer games. Games (or game DLC) get old, and people move onto the next, regardless of how good they are, leaving it as a "ghost town".

Making it so content can be run without needing a party of friends and/or a queue of 20+ minutes even when fed by roulettes... does not require making each and every piece of content to ever exist mandatory to complete weekly.

My point is that you need to give people a reason to go back to any of this 12+ year old content. Otherwise, why would they, when they did it already? You also can't necessarily make a roulette for a Field Operation or Cosmic Exploration. They're just not gonna be crowded eventually. As for needing others, it depends on the content type, since some are actually designed at their core for multiple players, but most things in this game end up being soloable, including Savage, dungeons, DD, variants and relics.

it's simply the bare and wasteful minimum of an ever-expanding experience that doesn't care about retaining accessibility or enjoyability for new players

Again most things can be done by players in the future still. I was just saying that it's mostly going to be a quiet experience (ie. 1-8 players) because players did the day1 rush thing that they do with all games.

There are mechanics you can build into the content to make up for the lack of PC's taking part in the content

Yes, but it won't replicate 144 people in Eureka or 72 people in Occult or Cosmic. Unless you'd be happy with 144 NPCs pretending to be players.

there are incentives that can be added in to make people go back, etc...

Like weeklies the way mogpendium is doing it? But again, it will still feel like a "ghost town" when you go back for whatever made you go back. Because the FOMO has gone.