I think you're remembering things more positively than they actually were. I think I could count the number of times I saw someone using trials gear that wasn't Messenger on one hand.
You remember how bad the perks were on the jewel? Icarus?
Ask Twilight or Unstable how they feel about actually being able to shoot stuff midair instead of Destiny's usual severe airborne accuracy penalties. That verticality was a huge part of TLW's appeal, especially for Strikers and Gunslingers. Some people even felt TLW had a hidden Icarus-like perk since it was actually viable in air.
As for people not using Trials gear, the sniper and shotty were straight up bad like you said. But elemental Scholars were great for Nightfalls and PoE. Trials rocket launcher was the PvP ideal, machine gun was also very viable. Jewel, Summoner and Exile's Curse were great representatives of their weapon types.
But that gets to the heart of this issue: the people designing the weapons are not the people balancing the sandbox. They designed a very strong, borderline ideal legendary PvP auto rifle. But the weapon sandbox was imbalanced so severely against ARs, and high-impact ones especially, there was no possible way to design a competitive AR. Jewel was a strong legendary HC and legendary HCs were good... but nobody used them because exotic HCs were dominant.
Point being they tried to make strong weapons, unlike now when they're intentionally designed to not stand out. And don't forget about the armor either. Getting a primary reload
and all special weapon reload perk on gauntlets? Plus having grenade throw and melee attack speed across gauntlets and helmet whereas now you can only have one. Chests with more special ammo instead of just sniper/shotgun/fusion/sidearm. Boots with two ammo types. Although I do like the new helmet and boot perks (Angel of mercy, last hope, second wind).
