that's your assumption; depression doesn't lead to 'being shinji' - complete infant, who understands nothing, wants nothing, does nothing, and says nothing...

I feel like most of those are at least partially false. Plenty of people go about life without really understanding relationships or much of anything and stay immature because of their lack of experiences and their self-pity, plenty of people who are depressed feel like they don't really want or care about anything either (that's one of the symptoms), and many of them are shut away and basically don't do much or are very proactive besides fulfilling their basic needs like eating/sleeping because they don't really care to do anything else, and a lot of the time those things happen all at once.

in the very least/essence, shinji is hyperbolic... (i've not seen anyone reach his level of pathetic, even those so-called 'people who run away from everything', because i wouldn't consider them pathetic to begin with).

What's the difference between them and someone like Shinji?

I mean you might make an argument that his character is a little exaggerated? That's not an entirely unreasonable position, although you might as well say that about 99% of anime characters, very very few of them are conceivable as people that actually exist, for the most part they're all exaggerations of specific traits rather than acting like a realistic person. In that regard Shinji's not that much different, he's just amplifying traits that tend to turn off a lot of people.

I mean, I have depression and while Shinji might be a little over-the-top I didn't find him especially farcical or anything, not moreso than the average anime character anyways.