No of course not since as far as I know there are no efficiency measurements of the BWR IGH at all. But the BSR has already a poor efficiency on its first and third ratios and the BWR can only be worse.

The difference in efficiency between 9, 10 and 11T aren't really big its the reason why nowadays all three main groupset manufacturers, SRAM-Shimano-Campagnolo offer cassettes with a 10t smallest cog and why Campagnolo has cassettes with a 9t smallest cog:

The issue that remains is the wear of the smaller cogs but its not a major issue since they aren't often used due to the fact they provide the seldom used highest gear inch.