I’d be very wary of any vendor supplied document, particularly a competitor, and keep an open mind. You can just as easily find a set of Microchip responses on this on Youtube.
And you should be wary of competitors claims and battles. That said, what TI claims here is mostly right.
As I said, these last few years have seen a rise in ultra-low power MCUs that really are way ahead of what we had just a few years back. As far as low-power is concerned, Microchip is behind for anything that requires some computing power. The Gecko line is behind now as well.
What matters of course is entirely dependant on your requirements, and mostly the overall duty cycle, that is the proportion of time during which your MCU is active to the total time.
Raw µA/MHz figures are an indication, but they don't mean much by themselves. What the MCU can achieve by MHz is equally important. A modern ultra-low power 32-bit MCU can execute on average more than 1 instruction per clock cycle, whereas the 8- and 16-bit architecture of PIC MCUs can only execute 0.25 or 0.5 instruction per clock cycle. So for the same required execution time you can lower your clock with most recent 32-bit MCUs and get much lower run current. I'd suggest trying an MSP432 dev kit or an STM32L4 nucleo board for instance, and see for yourself, you will probably be surprised.
If you only need to run your MCU at a very low frequency such as < 100 kHz for instance, this is the area where the ULP 32-bitters will be falling short.
Of course other considerations than power draw may also make you chose 8-bit or 16-bit MCUs, such as cost, available packages, and simplicity.