Quinn and Haseley were a non-traditional platoon, but if anything Haseley was the back-up. Quinn made 30 starts, including 17 against RHP. Haseley made 23, 21 of them against RHP. Not all of them in CF, sometimes they started the same game (and Harper and Moniak also played there).
Right now I wouldn't say either of them looks good enough to be a starting OF, in LF or CF. Haseley doesn't have the bat for LF or the glove for CF; the question is, which tool is he most likely to improve? But it still seems to me both Klentak and Girardi had already decided he's a 4th OF. Whether a new regime, or more modest competitive goals, changes that perspective, guess we'll see.
Not sure there's anything else to learn about Quinn though. Best-case he's a valuable bench player, worst-case he's Billy Hamilton.
A hodge-podge OF while they spend one more season treading water and seeing if any of these guys really have a future is okay, though if so, you still want Moniak.