Indeed! It's also ironic, in that a modern low Rds(on) mosfet may well have a smaller die and therefore a higher Rth_JC than the present part, and be worse for the job.
Unless, he's really thinking of lowering your 1V servod value, and figures a lower Rds(on) part would help make that work, that would be a reason for such a question.
A more current-capable mosfet would likely have higher transconductance at your 1A operating current, because it'd be closer to subthreshold operation.