Some of points in the OP come across as condescending and uncharitable to "causal" gamers--and seriously, in what universe is someone who played Destiny 1 to level 29 and complained about it on the internet about it a casual? Do you really need to sink 500+ hours into a game like Destiny to be considered core now? Where does that leave someone who has never visited a video game forum and only plays Candy Crush on their phone?
The notion that these kinds of gamers should be blamed for the shortcomings of Destiny 2 and dismissed as not knowing what they want is also off-putting. Gamers, even when lumped into sweeping categories like casual and hardcore, are not a homogeneous entity. The people who complained about Destiny 1 are not necessarily the same people who are complaining about Destiny 2. And even if they were, Bungie is ultimately responsible for the choice they make to cater to community feedback or stick to their guns.
Those general nitpicks aside, it'd be interesting to see hard data on the cash flows generated by the two kinds of Destiny players described in the OP to determine who really is the "addressable market." The season pass content and microtransactions purchased by the player base that sticks around undoubtedly has better ROI for Bungie, but does revenue from DLC and microtransactions exceed that generated by the entirety of the player base ("hardcore" and "casual") that purchases the base game? I don't know, but I imagine the initial player base (casuals and all) are a pretty important source of revenue for Bungie that shouldn't be taken for granted.