We shouldn't believe them because they are likely wrong now, not because they may have been in the past.
I've attempted to explain to you multiple times why your linear approach to future warming is wrong -- you are neglecting both negative aerosol forcing as well as the thermal inertia of the oceans. You also continue to assert that all climate models have overestimated the observed warming, but I wonder if you've actually done any proper analysis. If you have I'd love to take a look. My guess is that you are only comparing the IPCC ensemble average of ~0.2 K/decade with the current rate without even look at the individual model runs.
And finally, to fully appreciate your position, I'd like to again present a question you've yet to answer for me: Do you argue that the oceans cause the Earth to reach steady state more quickly than in the case of an oceanless (but otherwise identical) planet?
Let me go through this one more time:
1) Conventionally, there is really only one definition of steady state relating the energy budget at the TOA. Again, you can easily argue that the oceans prevent full equilibration from occurring realistically given finite fossil fuel reserves and the quick drawdown of atmospheric CO2 relative to deep ocean warming, but that doesn't reduce the temperature necessary for steady state.
2) Yes, I understand that the oceans require a great deal of energy to warm appreciably. So does everyone else. I can't figure out why you are trying to convince me of this -- the high heat capacity and low thermal conductivity of water is the very reason why equilibration time is so large, though the small k [and shallow MLD] is also a reason why we'll still see significant warming at the surface.
3) Simply because the oceans take a lot of energy to warm up that does not make them a negative feedback. Soil has a relatively low heat capacity, but that's not a feedback.
4) I don't and never have treated the oceans as a positive feedback. I did say that the "warming in the pipeline" is dependent on CS, and by simple thermodynamics, the farther we are from steady state the longer it takes to reach steady state. But equilibration time is also affected by effective diffusivity below the mixed layer, and even if CS is low, it still takes a... very long time to equilibrate.
And your linear approach to CS is still wrong. Human emissions of aerosols have reduced the net forcing at the top of the atmosphere, thus reducing the rate of warming we would see from CO2 alone. Your linear extrapolation also ignores that the fact that the rate in any one decade only reflects transient temperature change and not equilibrium temperature change.