Most likely they don't want to make the non-nesting species that easy to get. Tyranitar in tier 4 sold a lot of passes but it wrecked gen 2's longevity. We have no idea how long they plan to make gen 3 last.
You said it yourself, Claydol is challenging. I agree that their choices aren't perfect, but it's not the worst tier 3 choice since there's a definite audience for challenging solos.