I understand. But I'm sure you realize you changed the analysis so it's not the same income in both calculations as you
posted previously. It's $3,362 less in the current-law scenario. So of course the tax will be higher in the new-law scenario. For taxable income of $77,400 old-vs-new, tax will be lower under the new law. It has to be... every nominal rate is either down or flat.
Again, I understand the analytical logic for holding the Roth conversion equal. No question there is a negative impact from the lower deductions+exemptions that gets masked when you lower the Roth conversion. I'm in the same boat as I
posted earlier. In my mind, that negative impact occurs in the future at RMD time, as result of lower conversions today. Your analysis quantifies it now, which is fine. I sort-of implied the same in my original post, where I netted the two impacts.
As a practical matter, most of us with reduced SALT deductions will reduce Roth conversions accordingly to stay at the top of the 12% bracket. The lower rates will drive lower taxes vs current law. But the lower conversions mean higher RMDs and higher taxes in the future, a direct result of reduced SALT deductions today. In the grand scheme, these are pretty small numbers though. The original House version had the 12% bracket topping out at something like $92K, which would have been much better for us converters.