I'm unconvinced this comparison is very meaningful at all.
First of all, TDP is not the same thing as power consumption - it is a specification for the required performance of the heatsink/fan cooling solution.
For example: a Ryzen 3900X is a 105W TDP chip. Running at full speed on all 12 cores it consumes 146W; about 10W per core and the remainder for the rest of the package.
Secondly, it is entirely typical to run a single-threaded workload at a higher clock frequency (because if that's all you have to do, why not?), and chasing higher clock speeds is disproportionately expensive since it requires higher voltages, and dynamic power in a switching system increases with the square of voltage.
Again, taking the Ryzen 3900X: that's a nominal 3.8GHz processor. Running a single-threaded workload, it will typically boost up to 4.45GHz in testing. At that frequency, that single core is drawing nearly 18W - i.e. 80% more than at the nominal frequency achieved when all cores are busy and no boost headroom is available.
From what I've read about the A12/A13, the voltage/clock curves are particularly skewed at maximum clock speeds - something like 1.1V at 2.49GHz on the A12 and well under 0.8V at 2.3GHz - basically half the power to run at 93% of the clock speed.
There are a lot of unknowns here, but I think there are more reasons for optimism than your analysis suggests.