David, with respect I think you may be confusing yourself.
Axiomatically, no form of energy – is a ‘substance’ – neither heat, nor potential, nor kinetic energy. And yes, in strict terms “flow” is a metaphor, liable to mislead unless recognised as such – I believe the proper term is “flux”.
But none of this demotes “heat” from its status as a form of energy to the status of a mere “manifestation” of energy, as you claimed.
Heat is a form of energy. Temperature is a manifestation of heat.