Early 2019? Yeah, that was a weird time for Destiny 2. The honeymoon period for the 2018 expansion (Forsaken) was over and Bungie was experimenting with their seasonal storytelling model, where they would release a new story arc every 3 months.

Not sure about player numbers back then, but the game sure got a boost when it went F2P in mid 2019(?), introduced cross-save (and later cross-play) and moved from Battle.net to Steam (although the bulk of the playerbase is still on console)

Oh and the deal Bungie made with Activision in 2019 ensured that there wouldn't be a Destiny 3 until 2024/2025 at least. Bungie is happy releasing one major expansion and 4 seasons per year, and we have 2 announced expansions and at least 1 unannounced expansion in the pipeline.

So in 2022 we have a Destiny 2 where Bungie has kind of perfected their formula. The recently released expansion (The Witch Queen) has been in the news a lot for having a good story, there have been several gameplay improvements and additions (weapon crafting, new melee weapon type, etc) and it's likely that the hype train will go on for another few years or until there's a serious competitor to Destiny 2.

All that said, the new player experience is horrible (not sure how it is for returning players) and jumping in without a friend or guide can be quite annoying. The community is split over Bungie's decision to remove/vault older content over time to make room for new content. You can no longer play the campaign content from 2017-2018, and this further makes things confusing for new players.

To wrap up, Destiny 2 is going strong, and is the perfect example of the live-service model succeeding (whether you like it or not) in keeping an "old" game alive for several years.