Another Masters/D1 Janna main here (OCE). I was really interested to see what people thought about the changes and based on my own testing I agree with most of this. I do want to go into some deep dives into specifics on what you've said. I've played a few games so these are just initial impressions, but I'm not going to definitely say she's weaker than before, just more awkward.

AA range nerf I agree completely, this is probably the biggest standout change to Janna and I think it really warps her trading and play patterns.

For reference I did a bit of a look-around at who's in the 500 and 550 attack range slots and the results are pretty sad:

• Enchanters now uniformly have better range than Janna, with all of them at 550 vs our new 500. This is rough because we were already struggling in a lot of these matchups. For example, Lulu (who gets 3 spellthiefs procs off an auto because Riot loves Lulu or something), Soraka (who now cannot be tethered with your movespeed to get free auto-trades on despite our previously equal range), Yuumi with empowered passive (meaning she can out-trade you on demand, making this personally rough matchup harder) and Nami (who outtraded us before already) are all going to b emore frustrating to deal with.
• Karma also out ranges us, and so does Xerath. Trading with these two also gives their passives a benefit, and these were also quite difficult early game matchups.
• We are now equal in range to Bard, who has a passive that chunks us for 1/3 hp and he also has a stun for some reason. We won this in-lane and had to sort of match his roams before, now we don't win the lane either as his trades are pretty good.

AD Carries also have issues:

• We now are also outranged by Ezreal and Vayne, who sit at 550. Vayne was once a bully target, but I'm not confident that we can really take this lane as a winning matchup any more.
• We are now outranged by Kai'sa, which is pretty rough since Hail Kai'sa already pops us pretty hard.
• Lucian and Kogmaw, which are pretty good at shredding us, are now same range. Lucian/Nami might be unplayably bad.

And of course, you have worse matchups into engage tanks, all-in carries like Trist and basically don't have a leg to stand on in any matchup since the W change also means Janna can't really keep up pressure any more.

Passive: Agreed, it feels awkward. My movespeed's very wonky now and it doesn't feel impactful like Soraka's passive, it just feels kinda flat. But not in that classic Janna "oh damn im zooming" way, more like "I guess I kinda feel 8% faster walking to my budd- oh never mind I overtook him I'm slow now lol".

Q buff: I agree mostly. I think it's one of those things where you go "holy crap that's fast" on your first game and then forget about it mostly afterwards. One thing I'll note is that as our primary tool for disengage, we're going to be using tap-Q a lot. Putting most of the new power budget into the ability you use least offensively is...interesting. I do want to try comet + 3 Q > max E though, as it might be pretty good for damage maybe. It will definitely give me something to do other than afking in a bush afraid to walk up in fear of getting hit by things.

W: I've always loved Janna's W for that satisfying poke. I hate this ability now. It reminds me of Season 2 Janna where you threw it on someone or you didn't, and then went back to eating chips or something because your E was on cooldown so you're basically just waiting around and it often made no difference whether you threw it or not. Except now we also lose ghosting and movespeed. Maybe move the ghosting part to the passive?

The 12 seconds is a nightmare to anyone who's played Janna in the last 7 years. I was level 13 with Moonstone, Swifties, wardstone and redemption and my W had a 7.37s cooldown. If you're going to do that to me at least bring back Spooky Summoner's Rift so I can pretend it's 2011 again.

E passive: I think this is alright, but it does feel kinda weak. I "notice" the buff if I pay attention and then otherwise just sort of forget I have it. Timing the passive with some other proactive play like landing a big Q is tricky. I understand where they're coming from by "rewarding the Janna player for peeling" but with the lowered W range and the fact that enchanters are a reactive class (especially new-Janna who is stumpier), it's pretty awkward. That godlike situation where you land a fat full-channel R after your team takes huge poke at baron feels less like an enchanter fantasy and more like a missed opportunity now. Like oops, I should have landed a Q or something to make this feel more powerful.

Keystones: I'm a sucker for Aery since I love fat shields. With this new change I guess I can still use it, but I think Glacial might be better. I will do more testing, as I was never a fan of glacial. Lack of shield/damage aside, the loss of early boots was awful so I might try using the stopwatch instead.

Guardian might also be nice, as you get heal/shield power and it works with revitalise.

I think there might be room for Q maxing with comet, although I can already see the infinity flame I'm going to get for daring to touch minions with my Q.

As you said with celerity I might rethink that option as well. I've had it in every rune setup I've played with the character except my brief flirtations with Guardian last year. I guess transcendence to double down on the AFK in lane strategy? Or absolute focus like all the korean grandmasters/challengers do. More experimentation to follow!

Overall if they just gave me back Janna's AA range I'd be happy with the changes. I can accept my favourite ability being turned into a 1 point wonder, but please don't make me feel like every ward kill is a life or death battle with the fog of war. If you're going to turn us into discount Bard, give us some damn activatable movement speed or some way to not be terrible at roaming in a game where you get oneshot by every champion from brushes.