I really love the executioner models as well. But vulkan has it dead on. They really play completely at odds with the dark elf 'way'. Dark elves tend to field small units of infantry, which baffle most opponents, but then they turn around and dump 50-55 hatred poisoned attacks at high initiative. Attacks that might even be strength 8.
When you pass on wyches, you lose the frenzy, you lose the choppy, and you lose the high initiative. Of course you do gain armor and natural strength 6. But you are stuck with that T3 and only heavy armor. Now you are tempted to drop the ward save on them in combat, and now you lost the +1 attack. It starts going downhill from there.
If you want high strength combat units for those times that mindrazor isn't available then the executioners can provide that for you (but then so can hydras and cold one knights).
I could see using executioners as a dedicated monster hunter, giving them a flaming banner and then working out how many of them you would need to comfortably beat an abomination or a hydra. But I don't think I would ever use executioners for block on block combat. You'd need like 40 minimum. And witch elves could easily do the same anti-infantry work with 20-25.
Automatically Appended Next Post: Let me add that I think that you could invest less in the spearelves and more into the corsairs. Corsairs with the sea serpent standard end up putting out almost the same amount of hurt as witch elves and they have a better save. They just lose out on poison.
If you could find a way to get the corsairs up to 20, then they can put out 50 high initiative rerollable attacks with cauldron support. You've already got a supreme with tome of furion, so you can essentially guarantee having access to mindrazor... Does 50 strength 8 attacks at high initiative from a core unit sound good to you?
Those 25 spearelves look like they are built to grind. Dark elves don't grind well. I'd say to either drop them entirely for more crossbows, or make them 15 strong just for a sorceress bunker. 15 should be able to beat up most wizard killers, and it saves you 70 points. That and 5 points will get you 5 corsairs and the sea serpent standard.
Hope this is welcome and helpful advice.