I agree to a degree just looking stats overall, but I think it is fair to consider in Dragapult's case, it's so heavily specced into Speed that its intended role is to just hit decently hard while outrunning things rather than battering through things fresh like Salamence or Metagross would, while the gap between attack stats isn't as wide as something like Garchomp (which wasn't blisteringly so but had a speed advantage in its debut gen as well). They probably could have put 10 points into each of its defenses at the expense of SpA if they didn't intend for Special/Mixed to be an option (even if not the primary one), since it wouldn't be enough to shift Drag's role from a relatively-frail Fast Attacker.Tbh I don't think Dragapult counts as mixed attacker. It's clearly designed as phisical attacker, with the intentional design of not having a reliable ghost stab for balance reasons. Just people value a fast special attacker more due to the nuclear power of Draco Meteor and spammability of Shadow ball.
In both Gen 8 and 9, the only times actual Phisical dragapult was viable in VGC/BSS was if you were willing to commit dynamax/terastal to get the phisical ghost stab