Are level 16 corrupted Waystones still a thing

They are, but they are a pain in the dick to get.

You either spend a divine per map or corrupt all your T15s. I'd say about 80% of these corruptions stay at t15 or go down to 14 instead.

You can use the atlas passive that corrupts your maps again when you run them, which has similar results.

The loot isn't remarkably better than t15s. The experience is slightly higher, so instead of getting 3-7% per map you get closer to 10%.

It bugs me that once you hit level 92 the experience gain slows to an abysmal crawl....simply because the game forces you to engage with what is now "low level content."

Just corrupt a bunch of 15s and run the (few) resulting 16s and see if you notice a difference.

Yes. I sell them one for 1D+. It's pointless to run them.

Well they exist, but it feels bad if you can't get any reasonable amount by yourself tbh.

For negative rarity farming you want ilvl 82 items so they do have some uses for sure.

Yes

level 16 maps drop better loot, notice how when you run level 5 waystones they drop less exalts? Well level 16 drop more!