3d General circulation models and basic energy balance models are verified against range of temperatures, pressures, and atmospheric conditions in the Earth, Mars, Jupiter and Venus. The same model used for exoplanets is used to model paleo-Mars, paleo-Venus, and Titan. If the model is somehow completely wrong outside known limits, so is the parent model that is used in the Earth Climate change studies. The models work just fine at this level of required accuracy. You put parameters that describe the Earth, Mars or Venus into the and you get good description of atmosphere and climate in Venus and Mars that matches observations.
We don't have to model specific planets to get interesting information. In generally the interest is to model different categories of the planets and discover how their environments vary when we vary the parameters. It's possible to say something generic about tidally locked planets and their climate. This is what these simulations do.
GISS modelE GCM
ROCKE-3D version of GISS modelE GCM
Besides the examples you mention, research groups are now doing data assimilation for Mars (https://www2.physics.ox.ac.uk/research/geophysical-fluid-dyn... https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...).
Other groups are testing and improving models for Jupiter and Saturn, as you mention, based on various remote sensing observations. (For Saturn, see: https://theoryofclimate.sciencesconf.org/conference/theoryof...).
All of these cases have allowed modelers to observationally test their models and model physics against non-Earth conditions. This work has been going on for a decade now, but it somehow has not reached the technically-aware audience.
The case of tidally-locked planets is another step beyond the above solar-system planets. Thank you for the references you supplied, in your original comment, on GCMs for this case.
I enjoy modeling, and I think it's useful, interesting as well as respectable work. But a little humility would in science is always a good things.
Regardless, it's more useful to point to particular areas of uncertainty than to point to a general miasma of uncertainty around climate modeling as though nothing can be learned. It doesn't really move any conversations forward.
Just because we can't predict when an individual hurricane will occur doesn't mean that we can't predict "hurricane season".
edit: Apparently it's not even certain whether the Sun will engulf the Earth or not!