...is there's no reason to ever go spellthiefs over the targon's equivalent. Sure the last item has a small boost to AP but for most enchanters this is actually irrelevant. Given there's no CDR, no damage, no mana regen, etc. What possible reason do I have as a support to build a risk reward item when the non risk item can be stacked on average faster and there's no reward to begin with?
I've been able to stack the targon's item to 500 in about 8 mins while the spellthiefs item takes upwards of 10+ if you're even remotely against good players. This is going to quell interaction and make lanes static. I think you need to give some incentive with the risky item, that's why spellthief gave more gold overall in the past.
I'd like to hear Riot's reasoning on this because from what I can tell this whole change is super nonsensical with little to no forethought put into it.