As a new brewer, I can only share my anecdotal experience, which may or may not be relevant to this discussion. My first beer was a kit given to me for Christmas and bought from Amazon. My guess is the two biggest mistakes I made were the kit itself, which almost certainly had very old ingredients and oxidizing as I bottled. I left it in primary for three weeks and bottled without a secondary. The result was a drinkable beer but certainly not great. However, as the weeks and months have now gone on, I've found it to be almost undrinkable. It has definitely gotten progressively worse the longer it has been in the bottles, even with three weeks in primary. Now maybe it would have been undrinkable from the start had I not left it in primary for three weeks, but certainly it seems to me there are flaws/mistakes that can't be covered up by longer primary.
Sounds like oxidation,Im really not quite s hure what that is,but i think its a drying tastless effect which i think i may experince sometimes. Because i never get the wet/cardboard ever,however i do get a dried out tasteless effect sometimes which i think but am n0t certain is oxidation. Which may possibly be due to overcarbonation also which ive had a streak of.