(Powerbolt was a physical direct combat spell in SR5 as well.....)
Reason why it is direct rather than indirect is because you are hitting the target from within with destructive mana (like magically microwaving a hot dog).
It is very similar to Manabolt (which is described as inflicting massive cellular die off from radiation or necrotizing fasciitis,
but without the continuing effects).
Both are quite aggressive ;-)
In SR6 this mean that the target oppose the magic test with Willpower + Intuition and the damage cannot be resisted at all.
Clout, however, is actually forming a shockwave of kinetic energy. This is resolved as a ranged attack (where the target oppose the magic test with Reaction + Intuition like a regular ranged attack and the damage is also resisted as a regular ranged attack with Body).
Generally speaking direct combat spells (Manabolt, Powerbolt, Stunbolt) are better to use against feeble minded targets that might have really strong physical attributes. Depending on your reading, unlike indirect combat spells it might also not be immediately obvious from where the direct combat spell originated.
You could also say that indirect combat spells (clout, acid, fire, ice, lightning) depend a lot more on having a high magic rating than direct combat spells do (since indirect combat spells come with base damage equal to magic/2 (round up)).
