It may not claim to be but many of it's devotees do. Seriously, i've heard people calling this film a 'game changer'.
I haven't seen Parasite yet so I can't comment on that comparison. But to respond to your point about interesting stories being told in an entertaining way, I swear by that myself and think it's important so we can agree on that. But.
Here is my perhaps my biggest issue - The Joker may be an entertaining antagonist in the Batman lore, but he does not make for an interesting story simply because by attempting to humanise him, you immediately remove what it is that makes the character so appealing in the first place! Was it not simply fun and engaging to infer the way in which, say, Ledger's Joker came to be? Was it not more satisfying to revel in seeing a character with no capacity for logical thinking and a freedom that does not burden him with fear or remorse?
There are very subtle hints here and there from The Dark Knight as to what caused Ledger's Joker to be the way he was. I inferred that he was actually an Iraq vet who had been discharged due to war severe PTSD and his increasingly eccentric behaviour. He was maybe a prisoner of war too something hence his ability to organise ambushes and fighting prowess.
Now, you see how I got all of that through visual storytelling rather than being spoon-fed? And how much more engaging that is? This is exactly what Joker does NOT do. The film basically shows and tells you every step of the way that this guy is going nuts because we live in a sh*te society and its basically a serious of juxtapositions of that. Rough upbringing? Check, dodgy mum? Check. sh*t job? Check. sh*ttier 'mates'? Check. Object of affection who aren't interested in him? Check!
Now, if this film had told these sequences of events in a creative and exciting way like how Mendes and Deakins told a WW1 story, then i'd definitely be giving the film more slack, but it really doesn't. The framing is rudimentary, the lighting nice but in no way does it stand out. It's not daring enough to be 'dangerous' in the way that Lars Von Trier and Gasper Noe are, and it adds nothing to the mental illness argument other than suggestions that socio-political situations are the root cause of them.
Phoenix was great, but i'm sorry to say that the film was basic as can be.