My
Melee Arti build has a dc 99-103 on evocation (for Tactical Detonation) and it is working well in high reaper too. Not 100% tho but I am sure on low reaper diff somewhere between 90-100 Illusion dc should work.
As Ying wrote it is hard to build for both dc and melee dps/defence at the same time but not impossible to get a functional GCS dc.
You definetely need all the dc PLs and
this goggles to make it work at cap.
I think my build can be transformed to illusion focus instead of evocation but it will mostly work at cap.
Heroic leveling 1-14 is easier and much safer with a repeater anyway and after you can switch to melee and GCS.
If you go Deep Gnome 18 Arti/1 Ftr or DL or /1 Wizard you have a slot for Enlarge at lvl 1+ other filigree and ED setup should work.
You also can take the +3 Illusion dc int he racial tree for more DC.
Pros: Melee playstyle + GCS and/or TD is really fun! With one goggle swap you can use both spells.
Cons: Cant use GCS too early since you not building a caster. Gearfarming and minmaxing is a must for every 5 levels if you wanna be functional. Prolly it does not worth it to do the grind if you planning only 1 life to play with this build/style.