Scions don’t have battleline so you are limited to 3 of them. 3 scions, 3 command squads and 3 valks will be nowhere near 2k. It might not even break 1k. I'm thinking about starting pure. Valkyries currently *are* good, and they will be even better in 10th in spite of a nonsense special rule due to their massively upgraded durability and their rather excellent anti infantry firepower.
That said, one neat trick you might be able to pull is load 3 command squads filled with plasma or melta into a valk as a distraction carnifex of sorts, use it as a psychological threat for your.
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