The drawbacks of a "learning curve" in business, warfare, or any other operation are attrition (loss of trainees) or failure due to the success of your opponent due to a better or easier business model.
For example: During the Viet Nam era. Lyndon Johnson made a remark about the steep learning curve that the American G.I. was up against when fighting the gurilla tactics of the Viet Cong. This "learning curve" cost thousands of lives and ruined the lives of many young soldiers in the jungles of Viet Nam. Having a too steep learning curve creates waste and disaster in terms of lives lost, money lost, or time wasted while your business or war opponent has the advantage of continued success.
In today's market having too steep a learning curve is costly.
It costs a great deal to train an associate up to speed, only to have that person leave to pursue other opportunites, retire, or die.
It creates inconsistencies in the businesses as one site may be up to speed while others may be playing "catch-up".
It is quickly outdated. Businesses with a steep or protracted learning curve become quickly outdated as other businesses with a shorter or more agressive training approach catch-up and surpass the "traditional" business models with the classroom Professional development models