If you're looking for a firm that has a focus on CPG, you're probably already looking for small niche firms. Although the MBB's or T2's revenue is not focused on CPG (as a share of total), their absolute revenue from CPG is probably higher than that of those niche firms. And they work on more exciting projects for the larger brands.
So if you want to work in CPG, it's probably more exciting to look at the CP practices within the large and more diverse firms.