"a Frost start and then finishing with a talisman is very common to get the best of both worlds."
This is the problem imo. If talisman is a must have then it's unbalanced.
I disagree - If anything my scenario highlights that the gold generation from frost is so powerful it allows you to change to another item at a loss later in the game.
While the active from talisman is incredibly powerful it has very clear tradeoffs in both damage and gold generation. Frost Queens tradeoff is sacrificing talismans utility for increased damage and gold generation, and I find both items on equal footing, the current meta just makes a team speed buff more useful than an enemy slow super late game only because hyper mobile champions are in style (Draven, Yi, etc).
What I -do- see is a problem is that talisman is a valid start on all-in supports like thresh and leona - they should very clearly be getting face of the mountain which is, I believe, deliberately undertuned because of how game breaking it was on release.
The problem is not directly that Talisman gives so much utility, it's that Face of the mountain gives so little - it's HP shield is as dangerous to the support as it is helpful to the carry and makes best use scenarios complicated and feel bad in all conditions - I use it and I die but my carry lives, I failed. I dont use it and my carry dies but I live, I failed. Talismans I use it and we both die, I did all I could. I use it and we both lived, I succeeded.
Currently the picks are 10% Talisman, 5% Frost, 3% Mountain however with the Leona Thresh bot lane meta Talisman is stealing from Mountain and not Frost - it probably should be 5% Talisman, 5% frost, and 8% Mountain.