Seriously?

https://www.google.com.au/search?q=chess+engine+elo+rating

And we don't know "with 100% certainty", but we can calculate a projected win/loss probability using those ELO ratings[1]

A 3300 rated chess engine vs Carlsen at 2850 gives a 93% win probability to the chess computer.

That's roughly the same probability of an International Master raned player (ELO 2300) beating Carlsen.

The top ranked engine is Stockfish, rated 3500+

[1] http://www.bobnewell.net/nucleus/bnewell.php?itemid=279

ELO scores can only be compared across a single pool of players, and those scores you linked to are from computer v computer tournaments only. The absolute scores aren't comparable because you can effectively adjust the absolute score by adjusting the parameters you start the system off with.

As far as Im aware no engines compete against humans regularly enough to get an ELO score (presumably because watching a computer thrash human players for a few hundred games isnt that interesting).

Sure, the rating compression thing is a valid criticism.

There's little doubt they are much stronger than humans though. There are enough online games that if this wasn't so it would show up.

You haven't read the comments in your links, they say tuat this ELO was not calibrated with chess players which means it is not an ELO.

Arpad Elo's rating system has no single defined reference pool of players. The way it works is that you take a pool of players, establish the rating that unknown new players will receive (1500 in some cases) and then the system evolves from there. There are many disparate pools of players using the Elo system for their ratings, across many games.

Just because it was not calibrated with humans does not mean it is not an "Elo" system.