It's something that I've noticed as well. While I haven't seen the extremes that you have, C&S parcels are taking 1-2 days longer than "ordinary" parcels for me in recent week. Almost without exception the following timeframes have been -

Sunshine Coast to Brisbane. Next day for normal, 2 days for C&S.

Sunshine Coast to Sydney. 2 days for normal, 3-4 days for C&S.

It has admittedly not been a large sample size, perhaps 30 parcels or something but there is little question that my C&S parcels are slower than non C&S in recent times (was never a discrepancy, that I noticed anyway, prior to the past month or two).