The sort of system which would call for 16 transistors of the scale in question is perhaps not a good context to develop familiarity with the considerations involved, much in the same way and for similar reasons that a Koenigsegg on the Nurburgring is not a good context for a student driver’s first behind-the-wheel experience.
Be wary of such figures; they often do not mean what one might assume them to mean, as illustrated in this resource.
Power dissipated by a transistor is the product of the voltage appearing across it with the current flow through it, integrated over time. Estimations of this quantity can be made by considering conduction losses (those occurring when the transistor is in a stable “on” or “off” state, and switching losses which occur as a transistor is transitioning between the two.
It’s unclear how you understand the meanings of the Pd and Pc terms, but the underlying principle is correct; if the rate at which thermal energy is deposited into an object equals the rate at which thermal energy is drawn out of it, the object is in thermal equilibrium and does not (in principle) experience a temperature change. Practical reality is somewhat more complex. The resource mentioned above and its prequel (linked therein) attempt to illustrate some relevant considerations and processes for calculation.