If you want to see just how bad the Solar-based weapon treats your sweet can, in Curse of Osiris, here's a clip from iBLINKtv's Destiny 2: Curse of Osiris stream. Once you've done three of them, you'll unlock access to Heroic Adventures.
Curse of Osiris brings with it new high-level activities, a new level cap, and more - but for those that haven't purchased the latest content, all of the new end-game activities are now locked, even the higher level versions of pre-existing events like the Prestige Nightfall.
Destiny 2 players are up in arms yet again, now that the game's first expansion, Curse of Osiris, has been released: People who have not purchased the add-on are discovering that they can no longer play some of the game's high-level endgame content. These are more hard versions of standard Adventures with a recommended Power level of 300 and Nightfall-style Modifiers to contend with.
It seems like the heroic strike playlist is locked just because it's a feature that's new to Curse of Osiris. This will be addressed tomorrow via the weekly Bungie blog update. For years now, Destiny devotees have come to expect that they will need to buy all the game's expansions in order to keep up.
Activision and Bungie have not commented yet on this. If you're yet to collect your own, here's how to get Prometheus Lens in Destiny 2.