Urban legend has it that R’Yackov Kaminetzky Z’l once directed someone to R’Moshe Z’l to get a psak on a certain matter. The person alledgedly said that he doesn’t want any kulos, whereby R’ Yackov Z’l is reported to have answered if R’ Moshe says it is muttar it is not a kula, that is the halacha.
To say that “eruvin in general” rely on kulos is either ignorant or stupid. The rabbanim who permit its use may disagree with you, but are not lining up kulos to permit its use. Please see how some of the rishnim and achronim explain the concept “koach dihetera adif”.