With a decent rad set-up, it'll take ages to get hot. It's not a backwards step for a street car at all.
End of the day water cools better than air anyway. So on a 30 degree day, even if the water temp is 40 degrees it'll do a better job.
You show some data and i'll take my words back, but water will always cool MASSIVELY better than air. Get a decent size rad, decent sized core
Quite a few manu's from the factory use W2A, I'd take a guess mainly @ space saving vs performance given it would cost more, but hey, the Veyron uses it - can't be to shit!
The only disadvantages are weight, more complex installation and the cost. It wouldn't be simple and you would need to use decent parts & fittings for reliability where a A2A doesn't matter.
You'd also need to workout what motor & how much flow, vs the cooling etc.