Just regurgitating what Chris Rollins says, pineapples won't taste any better than the moment they are picked. It is kind of hard to test that theory.
A proper test would have a large collection of pineapples; eat some on Day 1 after picking, some on Day 2, some one Day 3, etc. You'd need a pretty large set of fruit to account for individual variation. The hardest part would be comparing across days, as taste is really hard to remember.
I suppose you could cut and freeze on Day 1, cut and freeze on Day 2, etc., and then have a double-blind tasting of all ages on Day 5, but that introduced freezing as a variable.
Would Brix and pH be a reliable test for . . . something? It's not strict proxy for taste, but at least it would be enough to disprove the "never gets any sweeter" theory.
In my personal experience/history (I've eat a store-bought pineapple 1-2 times/month) aging them on the counter for 2-5 days almost always pays off, assuming I selected a decent one to begin with. They definitely improve in exterior color and aroma.
The few I've eaten on Day 1 tend to be acidic and not very sweet.