Tenet may be a little less emotional than Dunkirk, but it’s also got a twistier and more complex plot and doubtless that was a totally different sort of challenge.
If you don’t believe me, just look into Elizabeth Debicki’s comments on the script.
As a bonus, what Kenneth Branagh is doing in Tenet is also a far cry from his Dunkirk character, which saw the actor playing a commander and someone who sticks around after the major battle to handle stuff–and did it with barely any script.