The claim that the amount of heat inside a body is physically meaningless is refuted by the principles of thermodynamics, which treat heat, thermal energy, and energy transfer as rigorously defined and measurable physical quantities.
The retrieved physics and thermodynamics papers consistently treat heat as a valid, measurable, and physically meaningful quantity involved in energy transfer, thermodynamic cycles, and system states. None of the papers support the assertion that heat inside a body is physically meaningless.