The main difficulty of the CQ is that it's a boss rush, with 6 servants to beat, each with two HP bars where the second bar turns them into alter egos. Breaking the bars also causes a large amount of various buffs and debuffs to go around while killing them outright strongly buffs the rest of the enemy team (including those in the back line), making it next to impossible to really plan your tactics around certain combos. You basically have to rush your attacks and hope for the best.

Personally I have no qualms about using command seals. It's a renewable resource and it helps me win, and it's not like anyone will complain to me about it.