This plan may sound appealing to people who know a little about the immune system, but the drawbacks are clear to people who know a lot about the immune system and also to people who don't know anything about it.
Arguably, the '1/2' in the drag equation is purely decorative, since drag coefficients are already unitless and could just as easily be half as big. Some derivations give more justification for the extra 1/2 than others, but one textbook just calls it 'a traditional tribute to Euler and Bernoulli.'