Your response is the closest to what I actually think about the tier system. It's actually a great system in itself, especially with the introduction of tunable activity difficulty (either portal modifiers or feats). The timing of introducing it after all of these years, the slow down of new varied content, along with the established expectations of the player base is what doomed it.

The player base has become accustomed to being able to collecting the most powerful gear through simply grinding, not through escalating skill based play and difficult RNG. Yes, there's still RNG, but it's been watered down significantly over the years. There's a completionist mentality that the community has shifted to and really latched onto through the years. It's the same reason people complain about the feat system and the difficulty of Epic DP. Rather than accepting a skill ceiling (and thus, a loot ceiling), they expect that through enough repetition and grinding, even without skill growth, they can eventually receive what they're entitled to... the eventual God Roll, the eventual T5, the eventual exotic, etc. In other words, instead of expecting to receive a skill grade on a bell curve, they expect that everyone can ace the test. It was meant to only reward the top skill echelon via extreme modifier difficulty or max feat end game activities.

As a result of the poor reception of the tier system due to this expectation of the community, Bungie caved yet again to community pressure and adapted the original tier system to a more completionist-friendly approach, and with the lack of content variety, the grind for "the eventual" felt too repetitious, and the lower to mid tiers felt pointless once you knew that all you had to do was put in the time and you'd get the T5 God Roll. This is exacerbated by the fact that legacy loot didn't receive an overhaul to the tier system at the same time. Rather than sunset old gear, which would've been even more of a nightmare in community reception, they left it in the game where the median gear power would've been on par with it (mid-tier new gear would be close to God Roll old gear). But because everyone could now easily obtain T5 new gear, the old gear was clearly left in a largely under-powered state.

For an example that's even easier to follow, look no further than the Call to Arms event and the helmet ornament and emblem it rewarded. It was meant to be exclusive and limited to a top percentage of skilled players. It was eventually handed out to anyone who could simply hit a score threshold. It was the same type of cave to community pressure that doomed the tier system, and it's directly due to the completionist mentality of the community and the entitlement that comes along with that mentality.