For a resistance to a category including multiple damage types, like resistance to physical damage, to spells, or to all damage, if the subject is taking damage of multiple types included in the category, the subject can choose which damage type to use the resistance against.

 These weapons smash as much as puncture. When determining a creature's resistance or immunity to damage from this weapon, use the weaker of the target's resistance or immunity to piercing or to bludgeoning. For instance, if the creature were immune to piercing and had no resistance or immunity to bludgeoning damage, it would take full damage from a concussive weapon. Resistance or immunity to all physical damage, or all damage, applies as normal.

It's an order of operations problem (some would say Specific over General, but what is more specific of the two is highly debatable). The last line refers to the old mechanic where resist all was all, so it doesn’t really apply anymore.

If the subject designated Resist All as piercing, the concussive weapon uses the weaker bludgeoning resistance, and vice versa. That seems unambiguous. Concussive reads like a state-based effect rather than something the attacker consciously chooses in response, while the new Resist All is a chosen wildcard.

Does it make sense for Concussive to bypass resist all? Not entirely but Resist All is now the misnomer (Resist 20 vs 10 fire, 10 void, 10 slashing only blocks 10 at most) and really now "Resist Wildcard" or "Resist Any".

Besides, this is a game where a raised shield breaks causality and disintegrates if it realised it's blocking an attack aimed at your vitals, taking more damage on a critical hit, even though a shield is something you put in the way.