RIP Achlyophage Symbiote, the only Gunslinger exotic worth using in year 1. Same thing happened to Young Ahamkara’s Spine when it got buffed to make it a competitive choice, but the tripmine grenades got nerfed as a result. Apparently, enough Warlocks don’t see an imitation patrol beacon in PvP to dodge them to justify their nerf.
Regarding Sunsingers, I think their main problem was that Bungie allowed repeating subclasses in Trials of Osiris. Bungie could have increased the tick rate to damage over time with firebolt grenades. The thing is that triple Sunsingers were too powerful in Trials of Osiris. Their win rate was something like 84%, which is a tad ridiculous. More frequent balances could have meant smaller steps to prevent nerfs being overdone.