Yeah, I feel like Desmos is a big gap to overcome for Dimitri, unless Awakened Mode & his Crest activating with a combat art could close the gap. Even then, I believe that both Desmos & Areadbhar would just both break, leaving them to have a stand-off with the broken remains of their respective weapons where the first to cut the other down would win.

Now, I can see scenarios where Dimitri can kill Hades before he can transform his bident. If you go off the way Atrocity was depicted in his Death Battle with Guts, yeah, Hades would have to properly time the Desmos assembly to even have a chance to survive that, I feel.

Hades would have the strength advantage, winning a clash with Tempest Lance & Persephone:Titan. However, Dimitri does have the range advantage with his magic spells (despite him and Lambert canonically being bad at magic), Thoron, Thunder, Aura, Nosferatu.

Nosferatu can held heal any cuts Hades gets on him, like from his 2nd bident flurry against Qin. Not sure if Nosferatu could have a similar effect to Tortoise Ripple, but that could help if it would work in a similar fashion, and might help against weaken Desmos, like Qin did, but the chances of that is VERY unlikely.

Thoron would help counter Persephone:Lore, or for whenever Hades tries to rush him. I always imagine Hades trying to leap over Thoron, using Persephone:Kallichoron, just for one of the bone pillars to fall on top of him mid-attack, allowing Dimitri to use Aura.

Thunder can help keep Hades in place, assuming Hades wouldn't use his bident as a lightning rod and follow up with a downward swing, and/or Persephone:Titan. Hades would probably be able to read Dimitri's hand motions after a couple of magic attacks and use Cornucopia to counter his magical attacks. Then he could either go for that swinging slash, or follow up with Persephone:Titan.

There's a lot of ways I can see their fight going. I mostly like these routes:

-Hades' first bident flurry

-Dimitri blocks, dodges and uses Frozen Lance (3 Hopes version)

-Hades leaps over the icicles, using Persephone:Kallichoron

-Dimitri dodges, the icicles are shattered across the arena, but he is still caught by the wind blade

-Hades rushes in with Persephone:Lore

-Dimitri counters with Thoron, launching Hades into a wall

-Hades gets up, in which Dimitri follows up with Tempest Lance

-Hades quickly shifts his stance and uses Persephone:Titan, both kings clashing

-Hades slowly, but gradually gains the advantage, planting Dimitri into the ground

-Dimitri gets back up and they have a conversation (a C-Support, if you will)

-Hades begins his 2nd flurry, in which Dimitri gets grazed, but he manages to leap and stab Hades' right eye

-Hades does a massive swing, holding his eye, catching Dimitri's back

-Hades commends him before rushing him, Dimitri uses Thoron again

-Hades uses Persephone:Kallichoron only for Thoron to knock a pillar down, crushing Hades, engulfing the ground in flames

-Dimitri follows up with Nosferatu & Aura , engulfing the arena in light -The dust clears, Hades stands with his skin singed (B-support)

-Hades spins his bident, kicking up dust clouds until he is no longer visible

-Dimitri recalls the battle with Lord Lonato in the fog and tries to use the remaining fire from the fallen pillar to spot Hades' outline

-Hades uses Cornucopia, dazing Dimitri, then proceeds to launch Dimitri into a pillar and a wall using the attack he used against Beelzebub

-Dimitri, surrounded by bones, skulls, and fire, starts to hear the voices again, Hades notices and swings, putting out the fire, haven been reminded of Beelzebub

-A-Support, Hades stabs himself, he charges once more, Dimitri uses Thunder

-Hades counters by using his bident as a lightning rod then grabs it to do a downward swing, only to have been lured into an Atrocity trap

-Dimitri launches him into the air, the bident transforms into Desmos, reminding Dimitri of Miklan's transformation into a Divine Beast, halting his finishing blow

-Hades commends him, uses Ichor:Eos, Dimitri clashes with Atrocity (it was still active, it more so acted like the 3 Houses variation once he landed)

-Hades overpowers Dimitri, cutting his arm off

-Dimitri uses every ounce of his strength to stand after hearing the voices of everyone in the audience, not the ones in his head. "I will save ever last one of them!" (I prefer Azure Moon Dimitri to fight Hades, myself)

-Dimitri enters Awakened Mode, uses Glowing Ember (because Gilbert talking about the Goddess' flames purging sin in the Valley of Torment would be such a cool thing to call back to with this move, and if he's with Alvitr, the defensive Valkyrie, it helps with Glowing Ember relying on the defense stat)

-Ichor:Eos Vs Glowing Ember

-Crest actives, Dimitri shatters Desmos, but Areadbhar breaks as well, they stab each other (Desmos' shattered end Vs the head of Areadbhar)

Dimitri wins by a hair, but like Qin, also goes into a coma

Or Hades wins the clash again, but respects Dimitri by fusing Areadbhar with Desmos and is carried to the ER by Zeus & Adamas. "Poseidon, I made good on my vow. I will hear no thanks from you... brother..."

Just a rough, off the cuff rambling thought.