Not necessarily best case, since both the UEF and GTVA have some tricks up their sleeves as well. And unless the Shivans came up with something new in that regard since Capella and AoA, the terrans and vasudans also have way superiour fighters and bombers.
A "real" fleet clash wouldn't be capital ships only after all.
The Narayanas torpedoes outrange the SRed, so in a scripted battle they would stay back out of range of those (which they don't do when only ordered to attack), having to fear only the BFReds. I don't know the ranges of the blue beams, but I could imagine the same is likely to be true for the Bellerophons BBlue and possibly for the Chimeras MBlue.
Since the Shivans didn't encounter AWACS in battle before (in FS2, they were only used to boost sensors, not for electronic warfare - except the Hamakos jamming, but that was against NTF and only radio jamming), those could also be very usefull for at least a few minutes untill the Shivans adapt. And in such a battle a few minutes can make a lot of difference.
Also there was no player action involved. Don't forget Humanity has Laporte, Samuel Bei and possibly two Alpha 1!