It's superior because it is safer. Not because the API (or requirement for using Lambda) looks better. The lambda allows the operation to work on the current state of the dataframe in the chained operation rather than the original dataframe. Alternatively, you could use .query("y > 0.5"). This also works on the current state of the dataframe.

(I'm the first to complain about the many warts in Pandas. Have written multiple books about it. This is annoying, but it is much better than [df.y > 0.5].)