I have thousands of hours in this game and think the game is utter garbage in some instances. Zero Hour though, as well as Whisper and whatever other timed missions there have been, are top tier content and I wish they were even more challenging as they used to be before. The timer is one of a few ways Bungie has found to increase the difficulty or at least the tension of content outside of raids, which are a larger time commitment and need more people, without just increasing damage and health of enemies. Since most of this content is jump-in-run, the gear requirements are minimal and it is easy to improve and track your progress with the timer. Low respawn timers make it possible to bruteforce add clear areas without highly optimized loadouts. Summarized: Skill issue.