By describing strong interactions between hadrons via a relativistic supermultiplet scheme and regarding weak interactions as a perturbation thereof, we derive expressions for nonleptonic weak decay amplitudes in terms of constituent quark masses and CKM angles, with no other parameters. Application of this method leads to ΔI = 1/2 dominance in some pseudoscalar meson decays if one scales down the couplings of heavy particles by √M mass factors, in keeping with heavy quark theory expectations. However, certain B and D decay processes to kaons are badly predicted and point to substantial soft gluon renormalisation effects in W-quark interactions.