Good is the enemy of deep
If you and I do not have a shared understanding as to what the word "good" means here, this statement becomes meaningless. Also, you have not mentioned or defined what did you mean by the word "long". Not everyone reads or **should** read texts in the same way.
Let me explain. The word "good" learning for me is a combination of an active exploration and a deep conversation with the author. That conversation can be in the form of challenging the author's contention, meaning, semantics, and advancing the arguments proferred in the text. In the process, I "absorb" the gist of the work, but also advance it in my own way. In order to do this, even a short (as in a 500 word essay) will take easily a couple of hours to interact with and engage. Does this mean that learning has not taken place?
Your understanding of the word "good learning" may be different from this perspective but what it is, you have not made it clear here. If you claim that all learning has to be in short bursts, that may work in some contexts, not everywhere. Sometimes you need a deep, long session with a piece of work examining and arguing every aspect of the essay/book/monograph etc. This is particularly true in scholarly fields where authors advance a thesis built on initial observations, theory building, careful examination of the premises. Breaking these into short "bursts" interferes with the continuity of examination of a body of evidence. In other settings, many readers get into a state of "flow", where engagement with an "apparently" difficult (to the laymen) topic invokes a sense of joy in reading and interacting and hours pass before you realise how time has gone. Does that mean learning has not happened? No.
So, being prescriptive about "length" of sessions and "goodness" without defining them upfront can create difficulties in the mind of readers (at least readers like me). Would you please care, if you read these responses, define them upfront please?