This is silly. The solution to a vitamin deficiency is vitamins. Clearly they're deficient while eating meat too, so that doesn't seem like a strong argument against plant based proteins.
[0] http://www.epic-oxford.org/publications/1554/serum-concentra...
No, they are not "clearly deficient while eating meat" as you claim. There's a documented B12 deficiency in vegans and vegetarians that isn't present in meat eaters.
> Omnivores had the lowest intake of Mg, vitamin C, vitamin E, niacin and folic acid. Vegans reported low intakes of Ca and a marginal consumption of the vitamins D and B12.