The myth probably arises from the very early days
of equilibrium change runs, where the ocean heat sink effect did not apply.
First let's define the «equilibrium climate sensitivity» as the «
equilibrium change in global mean surface temperature following a doubling of the atmospheric (equivalent) CO2 concentration.
In the real climate system, at any particular time the actual change in climate would lag behind the
corresponding equilibrium change for any given CO2 level, largely because of the thermal inertia of the oceans.
Their study
of equilibrium change can not provide such a constraint and so you seem to be taking them to task for simply not assuming that SLR can be rapid.
Climate sensitivity in its most basic form is defined as
the equilibrium change in global surface temperature that occurs in response to a climate forcing, or externally imposed perturbation of the planetary energy balance.
The climate sensitivity parameter (units: °C (W m - 2)-1) refers to
the equilibrium change in the annual mean global surface temperature following a unit change in radiative forcing.
Climate sensitivity - In Intergovernmental Panel on Climate Change (IPCC) reports, equilibrium climate sensitivity refers to
the equilibrium change in the annual mean global surface temperature following a doubling of the atmospheric equivalent carbon dioxide concentration.
Consider testing the climate sensitivity (CS,
equilibrium change in mean surface temp in response to a doubling of CO2.)