so treating holy priest and disc priest as a different class is a bit silly imo, it happens to classes with multiple dps specs too, one is usually gonna be better and pre legion it wasnt really hard to flex between specs. legion is the first xpac priest didnt have the choice to be the best healing spec basically.
shaman is filled with cooldowns which is really relevant for progress since the healers are usually undergeared and you pull through with cds. also it's not like their healing is hurt by having utility, it's still high. they can have windrush totem, the ress totem which doesnt count for a cr, 10% health, interrupt, which arent huge but makes them versatile. and link by itself puts you into the one of the best utility category. im not sure while you're talking as if it's not one of the strongest utility in the game if not the strongest.
none of the thing you listed for druid is exclusive for resto or even druid(cr is basically nothing since it's capped and 3-4 classes can do it) the only thing you can mention as an extra is movement and survivability, but it's not like you dont manage with a hpala or a shaman.
when paladins were bad "aoe" healers they were single handedly the best tank and single target healers and they were pretty much musthave in any raid. so im not sure, is this an argument of hpala being bad somehow? because it's not true. now they are not even bad at raid healing, kings at spothealing and again the best cooldowns possible and they heal burst really well. prot has cheesed so many fights in the past it's a really good utility. also the big thing they bring is devo aura, hello? which now flexes into being whatever you want. also beacons are just crazy all together.
yes heroic rag on 10 was solohealed by a resto druid but im not sure how that's relevant (also that was a very special case, it's not like everyone was doing it), ive never said resto druids have never been good before. but many times they have been bad. pala and shaman have never. also btw in the same raid you had to have disc and holy pala absorbs to kill the gate boss so resto druids were benched. or the spider boss where you had to have dmg reducions and link.
idk man, I actually dont understand how you possibly believe druid could be argued to be better than these classes now or even in the past over pala/shaman/priest (minus recently). I mean this arguement was much interesting during t19 when druid actually outperformed in healing, now it's not even that...