I used to like Sona vs enchanters and Janna vs engage. But at some point Janna seemed boring and useless and I'd rather just play Sona every game. A big reason is probably playing vs ranged supports, which is nice for Sona because you don't get engaged on but sucks for Janna because all she does well is disengage; her trades/sustain into ranged matchups is bad. You basically just sit there hoping you lose lane gracefully rather than terribly and your team wins.

But! Changes:

-Spellthief's (pbe): gold gen charge 10s->12s, mana regen 50%->25% spellthief's, 75%->50% frostfang, 115%->100% shard of true ice

-Engage supports (out): alistar, nautilus, pyke, rakan, thresh buffs - these buffs are not actually all that huge? they add scaling on stats (ap) which as supports these champs don't get much of because they're not really supposed to scale with items? But weird scaling buffs aside there are engage support buffs overall

So Janna unlike Sona and other ranged supports is fine with spellthiefs nerfs, she doesn't proc it as much and is never anywhere close to oom, and happy vs engage supports, which are not as good matchups as you might think but not as miserable as poke.

I also kinda like ingenious hunter Janna. Weirdly I don't think I've had a game yet with 2 crucible uses close enough that it actually matters, but shurelya's has felt surprisingly good (I thought Janna was better with moonstone but eh idk). Maybe into engage, crucible or even crucible rush will be better idk.

On the other hand you can kinda get away with sona into engage too. Shurelyas is probably better than moonstone since positioning around the engage matters more than the sustained fights you win anyways.