About Chopin's fourth Ballade:
Most of the piece is on a quaver unit and fast (con moto) but ritenuto are frequent.
Listening to several great pianists (such as Christian Zimmerman, Piotr Anderszewski, Luganski ...) they play the piece at approximately 130 semiquavers by minute.
This series of chords at bar 203 is preceded by a vigorous series of chords in quavers: six times quicker than the chords we talk about, with great intensity. The fifth chord has a duration of ten quarter notes on my edition (Henle).
They do not play this part exactly as I would have thought: they play the three first chords regularly but most of them a little faster than compared to the previous episode. The fourth is longer, a little softer, a little after the beat, like a ritenuto (which could be implied). The long fifth chord is played slightly more piano but not as long as the marked duration to my ears.
It seems that musicians have responded to this passage by managing a transition, a graduation, towards the longest length of the last chord approaching the total duration intended but leveling the differences of duration. Idil Biret and Murray Perahia are the interpretations I know that take this time graduation in the most direct manner, making it sensible as soon as the second chord.
So you might be right on with the general difficulty of slow time (in an ocean of fast notes) even as an expressive and artistic mean, many interprets are reluctant.
Despite the numerous pianists taking a different route, I think that the original duration contrast was intended by Chopin and is consistent with numerous episodes of fast tempo in the ballade but I do not know of a recorded interpretation where it is strictly respected, Cyprien Katsaris is perhaps the closest to what I understand of the text.