If I look at deliberate practice in musical proficiency amongst the general populace, it'll look like deliberate practice is responsible for almost all of the proficiency. However, if I look at the top 100 musicians in the world, they would have all practiced thousands of hours and I expect practice to have diminishing returns, so it should be responsible for very little of the variation in their ability.
I would expect also that in more multifactorial activities which are often the basis of professions that it is both A) difficult to ascertain what expertise is (often reducing to an empty social credential) B) difficult to evaluate what good deliberate practice is.
The meta-analysis talks about such factors as the predictability of the environment correlating with the effect size of deliberate practice. I think that's just the tip of the iceberg.