For a less gifted rider to complete a 300km in 15hours (let alone a 400km in say 25hours) is much more of an "endurance challenge" than 9 hours ridden flat out.
Peeps will argue that round in circles, but I'll stand by it! (I've done races at 10miles, 12h and 24h, so have some relevant anecdata to draw on).
On the other hand ... yes, a hillly 312km is a proper long bike ride. What's absurd is a commentator ignoring the long and varied tradition of similar (and harder) challenges on Planet Audax.
And finally ... the Mallorcan 312 looks a really good event. But I read about it in Cyclist (IIRC?) - the Comic should be covering such things, not obsessing about the various Etape incarnations and "epic" 90 milers in Leics.