I agree that they suck tremendously, a bit of a buff would be nice but you seem to want to make a falvor build viable.That's the thing, I don't want them to be able to melee well, I just want it to become realistic that they can survive melee........... frankly their attacks can be as weak as would justify such, but in reality..... the closest thing in DDO to a death knight tree is a combination between the Pale Master tree and the Eldritch Knight tree and if the Eldritch Knight tree is reorganized right, it might make possible for a reasonable powerful and reasonably weak imitation death knight build, it's all about making the possible skillpoint allocations in the enhancement trees only capable of so many combinations.
The reality of the build this would use, is that it most stresses defence........ fulfilling the defensive aspect could come with a tradeoff where the spells you are allowed to cast are reduced to a single school of your choice and a couple of utility spells such as dimension door and teleport (Basically only so your build does not hinder your traveling capabilities or let your team down when they expect you to cast dimension door).
The point is making the Wizard a class that more playstyles are compatible with as to clean up the waters some must tread through to get wizard past lives while also making the wizard at least somewhat fun in said playstyle, that being said.... a build can be fun to play but weak at the same time. Clerics can become quite formidable if you build them melee, but Clerics don't have access to all the spells a wizard would have, in fact you can make a wizard that only casts spells from a certain school and make them situationally decent. All of that being said it really wouldn't be rocket science to fix the Wizard and Sorcerer Eldritch knight trees.