It's a tradeoff because of the finite time for reading.
One can reread Shakespeare's 4 tragedies (Hamlet, King Lear, Othello, Macbeth) again for the 10th time (about 8 hours of reading) -- or -- read E.L. James "50 Shades of Grey" for the 1st time (also about ~8 hours of reading).
Some writers may suggest that you read E.L. James because that way, you can mark the checkbox of "read some BDSM material" and hence satisfy the "read more widely" advice. (The "widely" as the blog author interprets it). The blog and his quote of Seamus Heaney disagrees with that and advises to read what one enjoys. It's also ok if one is re-reading an old favorite again instead of unfamiliar writing that's often low quality.
And yes, choosing what to read is a zero-sum game. Mathematically, how could it not be?