I think part of my problem was buying all new PVC outers a few years back and also having a set up whereby a large amount of my record collection was stored on my TV unit, crucially above the telly, so the heat was probably greater there than anywhere else on the same unit (some beside and some below the TV).
I use the paper inners because many of these modern vinyls come in heavyweight vinyl, but do not have sufficiently strong inners (the printed/lyric ones) to hold the weight of the vinyl when in the post. I have lost count of the number of brand new records that have already gone through the inners before I have received them.
My current policy is to only really use polythene for non standard sleeves, such as things with an obi or gatefold sleeves. Basically any sleeves that can snag on other sleeves when getting them out of putting them away. The big drawback with polythene outers are that they are slippery so if I get a few records out at the same time the middle ones might slip from the parcel I've picked up.
Thoser Japanese single sheet 7" 'sleeves' or German promo info sheets fit very nicely into 7" polythene sleeves, but most 7" singles and their sleeves don't.
I'm simply trying to keep what I have in the best possible condition regardless of its condition when I received it. It isn't always easy.
Pledge