The research chiefs of betrothed drugmakers Pfizer Inc (PFE.N) and Allergan (AGN.N) say the proposed combination of their experimental drugs deserves more credit, including potential blockbuster treatments for schizophrenia and depression. Pfizer agreed in November to buy Botox-maker Allergan for $160 billion in a transaction meant to slash Pfizer’s tax rate and achieve other cost savings. The tax-inversion deal would shift Pfizer’s headquarters to Dublin and is slated to close in the second half of 2016.