I think Twice Born Star’s final nail in the coffin was when they changed the effect to only trigger if you popped a potion while in combat rather than proactively. This took it away from a lot of bombers or stealth builds that preferred to activate it before engaging to burst down an enemy.
You mean Clever Alchemist, and its actually a very popular PvP set even right now. They have since buffed both the spd/wpd and the duration of the set.
Heck with the 1 piece mythic items, its actually one of the better offensive sets that mesh well with those, since it can be 1 barred and has a good 4 piece bonus.
Oh, and adding to my previous comment, TBS is viable. Just not ideal in most situations is was once used for. Also as pointed out, CA is still a very useful set.
What is viable is often personal perception and just as frequently seems to be based on a narrow paradigm.