. Your statement about spellthiefs granting more than coin on Janna is false.
Tier 1:
Ancient Coin: 4 gold per nearby minion death.
- 6 minions spawn every 30 seconds, + 1 cannon every 3ed wave. That makes 19 minions in a 90 second window.
19*4 = 76 gold.
- Being away for any minion deaths reduces Coin's value. There's no mitigating factors in place to ease this.
Spell Thief's Edge: 2 gold per 10 seconds, 8 gold per 10 seconds on champion damage.
- Thief will passively generate 18 gold in that time. Assuming all charges are used: 8 gold * 9 10 second windows = 72.
54+18 = 90.
- Thief's requires damage on a champion, but has a 3 charge system to mitigate this and allow some leeway for roaming.
Tier 2:
Nomad's Medallion: 6 gold per minion death.
- We'll assume we've passed the 20 minute mark at this point and cannons spawn on alternating waves. 7+6+7 = 20*6 = 120 gold
FrostFang: passive 2per10 = 18. 15 per damage every 10 seconds.
Tier 3:
Talisman: Same values.
- We'll assume the 35 minute mark and cannons spawn every wave.
7+7+7=21*6 = 126 gold
Claim: Same values.
So under optimal use, FQC wins. And even if we throw in situational factors, FQC's added leeway in holding charges and procing on structures still gives it an edge.
You should not be poking enemies as Janna.
Unless you're against a really hard kill lane (ex: Leona/Draven) or a really heavy poke lane (ex: Cait/Zyra) that forces you to play on the back foot, you should be abusing you AA's. If you are in one of those scenarios, then go Coin. It's hard to harass if you're forced into permanent defense.
By mid game, any counter-engage you ward off will likely consume your stacks. You have lay-over time between consumption, but you also don't lose anything just because you decided to ward.
Talisman is superior on Janna than FQC or EOW, because it grants more utility on her.
It grants a move speed buff that is nice but unnecessary on her. The active is really strong, but she gets half of it's use from her passive. Gold permitting (not likely), you can get the other half from Righteous fury.
Though small, FQC adds chip damage to structures. The active is also invaluable for roaming since it not only chases and reveals the nearest enemy champions, it tells you what general direction they are in the moment you cast it.
What's more, FQC line lets you brush check very easily starting at tier 1. Any time you hit an enemy champion with an ability, it consumes a stack and you get the floating 15g icon - even if that ability wouldn't otherwise indicate them (Tornado in this case).
Talisman may have a stronger active, but FQC wins in quantity hands-down.
The coin line is purchased WAY more often than spellthiefs because it's universally better on her.
Pardon my straw-man for a moment.
MF Support is also being played way more than ever because of how OP it is. (>_>)