GK armies as a whole need as many models on the table as you can field. Definetly as many scoring units as possible. 20 terminators is impratical. If you are hit with a demolisher template that is probably 5-6 Terminators with a 5+ save, you just lost 200 pts in one shot. That also doesn't take into account small arms fire. Don't get me wrong, if the termies got there it would be brutal, but that is an if. Also the problem would be if they CC with a basic troop choice they would decimate it and probably not be locked in melée on your opponents turn and would get shot up. Drop atleast 10 termis for GK. Also you need some anti-tank in your list.
I need no anti tank. I am God. But really 40k has become too competitive. I for one play for fun. so what if I get slaughtered once in a while.