The Achilles' heel (or biggest disadvantage/pitfall) of relying heavily on alliances and cooperative strategies is

A. having to compromise the company's own priorities and strategies in reaching agreements with partners.
B. the added time and extra expenses associated with engaging in collaborative efforts.
C. the collaborative arrangements will not live up to expectation
D. Becoming dependent on other companies for essential expertise and capabilities.
E. That partner will not fully cooperate and share all they know, preferring instead of guard their most valuable information and protect their move valuable know-how.

Becoming dependent on other companies for essential expertise and capabilities.

Explanation:

When a firm comes in alliance with any other firm , the sole motive behind this is to complement each other with they key competencies. They make use of each other strength to grow together.

However it has one disadvantage is that if one rely only on alliance partner for the specific expertise or resources, it creates a sense of dependencies and if the alliance get annexed in future due to some reason, it can hamper the business.

In today's world example can be vividly seen, in Corona virus crisis, any  firm's alliance with Chinese companies may get hurt, as lock-down in china may interrupt major supplies from china.

answer; refusing to share information without the client's permission

answer; engaging in effective public relations;