Sona, being one of the most ideal support who can utilize and stack the Spellthief gold is completely inferior to just picking Coin up and playing her pre-rework Soraka passive (bleh)
The part where you mentioned you didn't want to have Coin be irrelevant to Spellthief, well you have accomplished the exact opposite and Coin now overshadows the shit over the Spellthief line
Annoyingly enough, you were warned about this
ChaddyFantome1 votesWhen the coin was reworked i knew immediately that it would be better on Sona because Sona is extremely mana consuming for a support. The mana coins are what make it so good on her and talisman active synergizes with her E.
That said, How the hell does that make spellthief irrelevant to coin? Talk about a leap in logic.
BlkStar1001 votesreads Ancient Coin's passive restores 15 % ... % ... Per .. cent . AWW SHET . Here comes the goddess of spams again crying tears of joy . No mo aram exclusive build . Time for the rift to embrace the old ways of the seraphs ... Welp , the moment i get back from my long holiday trip imma try it .
Kirius Dark1 votesIt's not just the regen but it makes sona level her ult sooner which is absolutely monstrous for the passive CDR at each rank up
SpaghettiVase1 votesits no longer a level up. Its a Janna passive now
Ferloren1 votesI do still avidly believe in the power of spellthief for the bonus movement speed on Q hit, which when doing a no-boots build I find to be quite useful. One reason why the coin is also so good is because of how bad the poke damage from spellthief is against a certain item 
