We have midcore content... just too little too late.

[Amarande]

It makes sense to classify midcore as content that has a fair chance of being cleared in one run, but has a high risk of leading into multiple wipes, or the run ending up in failure with randoms but not necessarily requiring much practice.
The only things that fall into that are Extreme trials, the instances within instances (BA, DR, Zadnor, etc), deep dungeon full clear and Unreals. Variant dungeons are significantly easier than that. While Criterion are already close to Savage in difficulty. They had the chance to make Criterion midcore, and they blew it. So have Savage and Savage-Savage instead. *slowclap*
But honestly if you enjoy deep dungeons there isn't exactly a complete lack of midcore content. If you don't... it's really dry.

And yet -

a) even "not much practice" is too much for most people for 8's, who will insist on the Duty Complete Wall rather than risking having to bring players up to speed.

(This may be on SE as well, because instead of having a full range of mid-difficulty content a la other MMOs, the reliance is on a single fight that you might have to farm up to 99 times and is similar length to a Savage fight, so the pressure to have a 100% reliable farm is pretty big - in fact, to the point that easier Savage fights are often more chill than EX, and likely this is entirely because of the fact that a given group only needs the one weekly kill to be pointful vs. an EX group that needs to get several clears in one session to be worth the time)

b) the problem with Deep Dungeons is logistical combined with the bubble gum and popsicle stick server structure.

You really gotta do it all in one go, which is especially punishing for POTD, because otherwise nine times out of ten you aren't going to get the group back together, so stopping "for today" is just a hard stop. HOH is a little bit better due to the fact that a complete run is only 8 level sets, vs. POTD where 8 level sets in, you're practically just beginning.

And then there's the fact that Deep Dungeons don't handle DCs gracefully at all - in a solo run, it ends it immediately even if you reconnect, and even in a party run the group frequently gets put out of sync badly enough that, at best, you can finish the current floor set but the save file is no longer usable.

Which happens painfully often, between SE's grumpy servers and the situation of American ISPs.

Which is sad, because the concept is really good.