While an attack is active, its priority is determined by a number of things. The positions of an attacker’s hitboxes and hurtboxes are first and foremost. Often, these areas overlap, so a fighter’s extended limb is both a weapon and a vulnerable area. If the limb’s hurtbox is intangible or invincible, the fighter’s vulnerable area is reduced. This second hypothetical move wins out if it encounters a typical first move, with intangible/invincible limbs overpowering those whose hitboxes and hurtboxes overlap without special properties.
Often, though, a fighter doesn’t have any intangible or invincible portions, but has something better: a hitbox that extends well beyond the vulnerable hurtbox. This is sometimes referred to as an attack having a “disjointed” hitbox, since the hitbox and hurtbox for the fighter don’t match.
This is usually found with fighters and moves that use items and weapons. For example, almost all the Fire Emblem warriors, plus adult Link, Toon Link, and Young Link, plus Cloud of Final Fantasy VII renown, plus Shulk of Xenoblade Chronicles… Look, pretty much anyone with a weapon. But there are plenty of instances of weaponless fighters who have exceptional hitboxes on an attack here or there, enabling them to safely swing beyond their vulnerable reach. This is the primary reason any “zair” air grab is useful, used as a low-damage but high-priority disjointed poke.