I want to put things into perspective for people who started playing with Beyond Light or Arrivals.
Before Beyond Light, seasonal content was only available during that season. It was "vaulted" the moment the season ended. Season of Dawn? You could only do Season of Dawn activities and earn the seal and the title between December 10th 2019 and March 9th 2020. After that, everything from that season was gone. Same with Season of Undying and Worthy (and Arrivals obviously, but that one was extended due to BL delay).
This was naturally unpopular as it pushed people to grind seasonal stuff in the 3 months the season was on so with Beyond Light, they changed seasonal content to be available during the entire year even after the season officially ended. The fact that we can still play Harbinger and Presage is something we wouldn't have been able to do under the old model. Being able to get the exotics and other gear, titles and seals and play the activities, all of that was not possible before they changed the seasonal model.
I'm not sure what else Bungie can do here unless we want the game to be funcionally unplayable due to overbloating it with past content. We've seen what that does to a game, and not just for consoles. Destiny 2 before DCV was very slow, too big and it was straining people's PCs as well as consoles. You can't keep adding content to the game indefinitely. There's a limit to the engine.
Keeping seasonal stuff all year long is the best we can get unless we want Bungie to make a completely new and separate game every year where we'll have to start from scratch every year. This is obviously ludicrous AND it doesn't solve the problem of old content being gone because if the games are separate, old content won't be in the new game anyway.
Currently, we're losing an outdated campaign that's 3 years old (which is also the only thing left over from Activision era: good riddance, no matter how good the campaign is), 2 strikes and 1 destination which is not used for anything besides the aforementioned campaign and Spider's material exchange (which is highly inaccessible because it requires people to go from the tower to the Tangled Shore and back just to do the exchange so they can purchase stuff in the Tower: moving the material exchange to the Tower is something that should've been done ages ago).
We are getting: a new campaign, most likely 2 new destinations, ?? amount of new strikes and, from the article "we’re bringing a carefully curated selection of content out of the DCV, including a classic raid, two PVP maps from Destiny 2, and one classic PVP map from the original Destiny. We’re excited to share more details on all of this in the months ahead." Meaning, we'll know more details about all new content coming to the game later.
I understand people being upset, especially when it comes to things they paid for. But I would also like to note that I'm pretty sure everyone played through this content more than enough to get their money's worth for what they paid. I'm not sure how many hours of replaying Forsaken people think is enough to get their money's worth, but surely replaying it at least once with every character is enough. We do the same with singleplayer games; we play through and then we deinstall. There's like almost 5 months left of this content staying in the game so if people are worried about getting their money's worth, they can replay the content for another 500 hours for sure. I'm pretty sure it's reasonable to assume that would be worth the money spent on the expansion. Or, if they don't have it yet, it will be free from December to February.
And of course, when it comes to seasonal stuff leaving, we knew that. We had it much better this year with the content staying for a whole year instead of being gone after 3 months. It's what we asked for. We can't expect seasons Hunt-Lost to stay going into Witch Queen. There has to be space made for seasons coming in WQ.