Dual YT-1300s definitely did enjoy a period of dominance, as did B-wings, and TIE fighters.
Anyway, I don't think anyone believes ordnance is useless; rather they think that it is awkward, inefficient, and overshadowed by better offensive upgrades. Extended munitions help make ordnance carriers more cost effective by allowing more ordnance to be brought at a reduced price, but does not solve other key problems with ordnance, and in itself requires substantial investment.