Here are the actual problems, and not the bullshit ones people are making up as we go along.
1) Druids need a defining debuff that fits with their role as a healer, and a niche. Being an underpowered cleric, is not a niche, and is in fact a joke. Archaic is awesome, don't get me wrong. Too many people have no idea how useful it actually is, and many druids just don't fucking cast it. Which is stupid. So so stupid.
2) Cascading vim, is not good. Personally I don't even see a reason I would keep it up most of the time if I had it. It's horribly inefficient, and tries to do multiple things, and does none of them well.
A note about druid dps. If you're nightfiring, you're doing it wrong. Unless you need it dead fucking pronto, and there are other classes for that. Our dots are actually pretty fucking great because of their super reliability. There are many places actually, having extensively played shamans as well, where your poison dot will absolutely refuse to land. I can think of like 2 places where druid dot has any difficulty landing whatsoever, and it is because the mobs are actually immune to magic, and/or spells.
The pet sounds fine, a small heal added to it would really just be completely annoying, and end up fucking up timing, and cockblocking parts of your heals. Recall minion for druids however, is a great idea, and if we have a serious pet now, we should get something like it.
Their buffs however, are fucking fine.
Roots and snares used to be good, before everything in the game summoned. The few times I've used snares on raids as a druid were the best times I've had one one, because we're snarechampions
Tbh if shamans had slightly more healing power and a group heal, or you could have 4 clerics on a raid, druids wouldn't even get used. So I'm divided. We are not a jack of all trades however. We do a small amount of dps, comparable to the dps the other healing classes do. So unless shamans and clerics have suddenly also become jack of all trades classes I think we got fucked over.
I know people vilify the gheal all the time, but in my experience it's easy enough to time if you know how the fight is going to work. The trouble comes from lack of ghots. Hots enable clerics to accomplish two things at once and they let clerics play more less reactively than the other healers.
Typical group healing comes in the form of slow, steady AE damage, or large and periodic damage. Almost never does a group take AEs so rapidly that a group heal is necessary from 100% life. If druids has a regen spell with a long duration, say 1-2 minutes which healed for 300-500 per tick it would give them a new niche and a unique spell.
Untasid: Not being able to go to certain encounters is just the most obvious example of why druids are bad. If, like you say, the encounters are the problem, then the only solution encounter-wise would be to simply make the fights easier. You can't design content specifically for a druid because a druid doesn't do any particular role well enough that a different class couldn't simply replace them.
The druid groupheal isn't too hard to predict granted, IF you know what is going to happen, but it's a major slash across the throat of the druid's healing power, and OMFG I NEED TO SAVE EVERYONE NOW ability. In most of the more difficult content this is like taking a knife to a gunfight. A druid is a crippled healer. If you get a bunch of adds, a druid is fucked, whereas while using eldo, I've barely batted an eyelash until i hit 15m. Even if you have an idea of what is going to happen, you cannot predict every single thing. Clerics can save you even when shit hits the fan, druids are not good at that. Shamans are good at that in a different way, like a long distance runner.
Grouphots are only part of that. Hots are amazing, and really I don't think clerics should be as good at them as they are. Druids should also get them. They do allow playing less reactively, but you can't possibly say with a straight face that being able to heal the group completely twice in the time it takes to cast one group heal that heals for less isn't a problem.
Part of the problem is that clerics are used for fucking everything is there is no competition at all. The only reason to take a shaman instead of another cleric is slow, or if you cannot find another cleric.
The biggest problem with said encounters isn't that a class is bad or good, it's that it takes 30 fucking years to get there and if you wipe you're fucked and I hope you enjoy doing the whole thing over. A mistake that 6man content such as cmal did not make, and something that seriously cripples the fun of doing any of it.