Eh, I don't know. All of those are still Weapon Qualifier attacks, so they can be defended against with Parry, Evade, Dodge, or Weapon Shield, plus an appropriate Cloak or Bane; Stun/Destruction Blow isn't a Strike, either, so it can just be blocked normally with a weapon or shield. In contrast, Spells can only be defended against with Dodge, Spell Shield, or Spell Reflect, plus an appropriate Cloak or Bane, and the Shield and Reflect are both in the upper half of spell levels (5th and 7th). The ability to defend against an attack has some effect on how much it costs, and I don't think that's a bad thing.
It's also an incredibly useful skill for Spellswords because you no longer have to carry around packets for spells if you have enough purchases of this and enough Martial XP spent to be able to Spell Strike any spell you have memorized, nor do you have to let go of your weapon or shield to cast them; it only takes 100 Martial XP to Spell Strike any spell up to 5th level, and only 200 XP to be able to Spell Strike any spell at all. The utility that grants is amazing for a skill that only costs 3 XP (and also counts towards the Martial XP requirements to Spell Strike higher level spells). Every 7 purchases also costs enough Martial XP to qualify for the 8th, although you're not likely to buy that many unless this is something you want to focus on.
For the record, you'd have to reach almost level 30 to have both a 9th level spell slot and enough Martial XP invested to Spell Strike it, but for every spell level lower than that you can reach it about 4 levels earlier. If you're very efficient with your skill purchases, you can be able to Spell Strike a 5th level spell by about level 14. (You'd need 30 purchases to be able to Spell Strike every spell in a pyramid with only 1 9th level spell, which is nearly half of the Martial XP required to Spell Strike a 9th level spell.)
ETA: I purposefully left Resists out of the possible defenses, since those are Racial and not available to every character.