I do wordle, strands and, when available (once a week) I do the midi.

Wordle and strands together usually take less than 5m. The midi ranges from 3m30 (my best time) to ~12m (my worst).

Not done Letterbox, Pips and Tiles, but I figured that all their puzzles are at the same level of difficulty.

It's interesting, to me, that (from my reading of the paper, which was very quick) they they consider it hard/easy based on a sort of brute-force attempt to find all the answers.

There is a theory that for a puzzle game to interesting it has to be NP-hard. Something about how otherwise your brain is too good a latching onto the "trick" and the game is boring.

They are difficult. As I'm not a native English speaker, I didn't know many of the obscure words or usages, so I actually played these games from a purely computational perspective. I discovered early on that there were a lot of at least NPC problems in them. As my English improved (partially thanks to these games), intuitions began to help me take shortcuts, as if I had become a nondeterministic Turing machine.