The let’s say hoplite image you’re having in mind was likely more because of their helmet and the shield + spear combination? I would assume.
It certainly has elements of it and gives the Stormwind troops a really good looking let’s say “imperial” look.
Almost medieval (the full plate definitely is more like that) but with the barbubte like helmets it also gives an ancient feeling to it. A nice mixture for a fantasy kingdom in my view.
Just some things that I can observe, feel free to say were you may disagree.
Let’s take a look and use this as a basis (couldn’t get a good one from the cinematic). It’s from the movie:
https://wow.zamimg.com/uploads/screenshots/normal/740080.jpg
Going only for this helmet it looks like a barbute with a strong “Corinthian” influence. Not so much from the real design, more from the fantasy of it and the crest, or tail.
https://collectionapi.metmuseum.org/api/collection/v1/iiif/24692/1521993/main-image
https://upload.wikimedia.org/wikipedia/commons/thumb/2/26/Barbute_MET_DP-12880-047.jpg/1200px-Barbute_MET_DP-12880-047.jpg
The mail is likely from a later date than the Norman invasion of England, not much earlier because of it’s long selves.
The pauldrons are clearly inspired form jousting ones, or direct based for cavalry fights. The higher part on the (left) shoulder was made in the hope to catch an enemies lance before it could hit the head. It’s a stable in fantasy.
Now comes the tricky part. The breast and back plates. I would say the inspiration is still a late medieval 14-15 century breast plate. But it’s so different in it’s own ways.
Especially since the stomach isn’t covert. I could see something like this happen mostly if soldiers had to supply their own armors like during the very early Roman Republic. Or if Stormwind was perhaps short on supplies or money (though I don’t think it “saves” much).
https://www.by-the-sword.com/images/product/large/AH-6088B.jpg
Something like this isn’t a great armor obviously. But it’s better than nothing and with mail underneath not a terrible start (for arguments sake).
But that’s not the inspiration.
Another form of armor comes also to mind. More something like a mirror armor. There existed a lot of different types. This is only one example of many.
https://i.pinimg.com/564x/69/2e/09/692e09309a9c3b37469e9e905e221e4b.jpg
The connection I see here are the exposed part of the torso and the smaller plates.
At the end I would say the inspiration is simply a +/- 14 century-ish random knight:
https://i.pinimg.com/originals/ce/d4/a4/ced4a40072a196815d9f754c080031e7.jpg
With a barbute (would work for footman and is historic accurate) and a heater shield. Sometimes they are so big their height resembles almost more a kite shield (way earlier than the armor).
Fun fact Anduins lion helmet has a historical counterpart.
https://i.pinimg.com/originals/f6/0b/3b/f60b3b4860262ae533e4b91f0c45dc46.jpg
https://upload.wikimedia.org/wikipedia/commons/1/1f/WLA_metmuseum_Lion_Head_Sallet.jpg
It’s also not really new: https://i.ytimg.com/vi/NCs91xnK43E/maxresdefault.jpg