Not true. On HM certain enemies such as enemy Swordmasters, Gwyllgi, and Draco Zombies would most likely doubled attacking the Valkyrie's. And yes, somewhat low spd is a disadvantage for them when confronting lets say either the enemy Swordmasters, Gwyllgi, and Draco Zombies because they can double attack Valkyrie's. And theres clearly no way Valkyries can dodge from their attacks at all seeing as their Spd cap is really low when confronting those enemies during battle when carrying such higher Wgh tomes. And most likely those enemies would dodge the Valkyries attacks since they have to carry such heavy tomes and that Spd and Con is what's getting in their ways. Also Valkyrie's have really poor HP growth.
Also...why in the world you even bringing up infinite stat boosters topic? That's just cheap talk. If your going to do that then theres no sense of debating. L'Arachel was meant to have 6 Cons to begin with.