The survivalist is actually quite a nice fit for your set-up. Their Multi-shot and Finishing Shot add more attacks per turn, which sets off more activations of Links, which can get up to 9 activations with a maxed Improved Link. And in the turns where the Landsknecht is only setting up their attacks, or recovering from ailments and binds that block their moves, the Survivalist can use their Evasion-based Skills to set up for Hazy Shot, which deals massive damage, if maxed out, at a reasonable price. Drop Shot and Sagittarius Shot also deal great damage on their own, especially as Drop Shot gets tripled if it hits an enemy in the back row.

Survivalists are generally supposed to be good additions to the party that has already covered the essentials, providing some small, unique assistance and good damage. Skills like Efficiency and Quick Step make light of that. Their strength is not their raw damage, even if they're quite good at that, they excel at being a supporter in a less traditional sense. (For example, the Sovereign would be a more traditional supporter, using buffs and heals to directly assist the party.)