I think it heavily depends on type and quality of content so it would be nearly impossible to give a correct answer to this question.
It is true, with the attention spans that short it is hard to keep going through many long articles though i seldom find that problematic when reading your posts especially when i'm interested in the topic or can relate to it. Being honest, I've skimmed through some of them but spent more than average on the others, but that's the way we filter and consume content i guess.
For entertainment purposes i prefer short to medium (written content with illustrations). For educational well written pieces i do not mind long at all and naturally prefer longer ones with more detail in it.
So as for a platform, mix is better, as for an author, they have a pattern and that depends.
Thought i have noticed a few times, especially when i sat down and put up a long article, that it would get less engagement (not necessarily rewards as length might trigger some curation trails) as they might look intimidating (as your brain calculates available time and time needed for task completion then compares it to medium of information relevance and discards it).
But in general my comments under your posts are longer than my owns posts by far :) So there is another question. How long should the comments be :)
This is also how I write - I don't expect people to ponder every word, just find an area that they find interesting and build some thought upon it. It is nice when they relate it to the general arch also though :D
Yep. People have to play their part, the part they are suited for, experiment if they want, but find their place. Not everyone is going to be able to play every role.
I find that long content (in general) doesn't get as many comments, but the comments are of much more substance than the short.
That's because people that are really interest give it mo time and thought.