From what I found on the internet, A350s all have the better cabin pressure, but not all have humidifiers.

Some digging around the pilot forums, some are adamant Delta didn’t spring for the humidifiers. Others point out that humidifiers are in the tech manual, so maybe they just sprung for them in the passenger cabin? Everyone agrees it is all very contradictory. There is also general agreement that LATAM did not spring for them.

My last long haul was on a 787, and I felt way better after those flights than I have on any other plane. I’llsee if the lack of humidifiers make a difference on the A35L trip coming up.