Hives also have the possibility to move build power very fast. Buidling ras boys, and just before enemy army arrives, throwing up experimental. Or Building units, and just when enemy scouts have passed, throwing everything into building a nuke. Etc.
Hives also have self upgrading capacity, that allows to add very much build power in short time, without engineer/trafficjams.
So, yes, Cybran hives seem very strong ,on some maps. But they are not detrimental on other maps , as Cybran has no obligation of using those. For quite low cost (?) 14 mass for 1 bp. While t3 engie costs 10,4 mass for 1 bp.
Making hives more expensive could reduce the advantage of Cybran. But idea could be also to give different hives for Aeon and Sera. Less range, hp, cost. Or more range and no upgrade. Watch out for too much range, as they become defensive arms.