I think the fondamental difference between classic and modern Chris is classic Chris was completely unaware he was a retarded manbaby. Yes, he did actively shun growing up, but the combination of poorly addressed autism, complacent behaviour from his family and few "friends", social isolation and spoiling from his parents convinced him that this was all completely normal. He lived his adolescence and early adulthood the same way a kid expects to live them (i.e., the same as being a child but in a bigger body and with a CUTE GIRL HIS AGE), and believed reality worked like saturday morning cartoons because nobody ever told him otherwise. Classic Chris was entertaining because it's funny to poke at a reprehensible fat dimwit who is really an adult body inhabited by a 7-year old who happens to know about sex but has no idea how anything else actually works.
Modern Chris has been forcibly exposed to the real world and instead of living an extended childhood like he did in 2007, he is trying to live it. He's basically in cope mode and I think it shows in how he's gradually become more delusional and yet less energetic about his interests. Like how Sonichu has become his religion and yet he got tired of making comics.