Covering defender? Yes. One. Defender.
Replace Courtois with a defender making a dreadful tackle as the player comes in on goal with just the GK to beat after. That's the precise definition of DOGSO.
Why do we think to treat it differently when a GK makes that tackle, fouling the player. "Well, there was a (single) covering defender... "
No, no, no, no. The GK is a far better defender of the goal than a field player... why? Because the ******* can handle the ball in his own penalty area!
And yet? Clear DOGSO. Be consistent, please.
(and pardon my ranting on this one, it happens far too often here where the GK gets a "free pass" because there's a defender somewhere in the picture... and NOBODY ELSE)