None of that matters. You are focusing on the wrong metrics. What matters is the total CO2 emissions projected by RCP8.5. Those projections most accurately reflect observations, that is a simple fact. RCP8.5 may have gotten wrong the reasons why CO2 emissions are high, but so far its total CO2 emissions projections have been more accurate than the other RCP scenarios.
Note that the RCPs have been replaced by the SSP scenarios. SSP5 has similar CO2 projections as RCP8.5, but uses a different pathway to get there. SSP5 projects a booming global economy, moderate population growth, and growing materialism in the developing world that is mostly based on fossil fuels. It seems similar to the Nordhaus scenario.
You appear to be extraordinarily confident that the worst case scenario is virtually impossible. You really have no basis for believing that. I’ll give you two graphs explaining why.
The first shows global emissions from 1990-2021. Do you really see convincing evidence that the rate of emissions has declined? Perhaps it has, but we probably need at least another decade of data to show it statistically. The fact that it is not obvious probably means that whatever mitigation is occurring is not enough.
The second show the correlation between Global GDP and CO2 emissions. GDP growth appears to be the main driver of emissions. Until there is a significant and consistent decoupling, an expanding global economy will lead to the RCP8.5 levels of emissions. Currently, evidence at the global level that GDP can grow without rising CO2 rates is, shall we say, sparse.
My take from all of this is that significantly more mitigation needs to be done to avoid a high probability of climate catastrophe. I believe that is the general view of the climate science community.