In most, if not all, mmo/loot games, you don't get the option to upgrade any of your old gear to the new "cap", whenever an expansion or patch that raises the ceiling for gear is released. Which essentially renders all your previously collected items useless.
Level 60 gear in D3 is garbage on level 70
Level 90 Mists of Pandaria gear in WoW is garbage at level 100 in Warlords of Draenor
Level 50 gear in Borderlands 2 is garbage with the level 60 dlc
etc.
Bungie allowing you to upgrade exotics to level 32 is "respecting your time" far more than any other similar games do.
And I say this as someone who thinks Destiny is terrible btw.
In general, I'm fine with a new expansion raising the level cap and thus causing some gear to be less useful. The problem with Destiny, as compared to those games, is:
-It has a lot less gear and less varied gear. Only Exotics look unique--most Legendaries are reskins of each other.
-RNG makes it feel like Exotics, and Raid legendaries, are more valuable than they are. Some players have played for 100 hours and still don't have any Exotic bounties. Some players have played the VoG raid ~20 times and still don't have certain pieces of Raid gear
-There is shit all to do in the endgame, so taking away the only thing you can make progress toward (your gear) feels like an extra kick to the nuts
The time between expansions isn't typically only 3 months. Making gear obsolete every three months is bad game design. And that's considering you're lucky enough to get a drop and use it that long before it's obsolete.
This. RNG and the time between these expansions (as well as the lack of content, going off of The Dark Below) makes it worse than other MMOs. Because there is so little to do, all you have to look forward to is getting new gear, while knowing fully that it will be obsolete in a short amount of time.