The short answer - it should have both revenues and costs. What you are saying is not a hypothesis.
The major mistake of the candidates is that they start using the hypothesis and neglect having a proper structure.
Moreover, if you perfectly solve the case without ever stating a hypothesis - you'll pass the interview. So most probably you had some other issues with the case as well and they used it as a standard feedback.
There are two ways to use the hypothesis:
First - presenting a structure using the hypothesis. For example, if you are having a PE (private equity) case, you should do the following:
1) Make classic structure (market, company, competitors, feasibility of exit)
2) Make subpoints (e.g. in market: size, growth rates, profitability, segmentation, etc)
3) Present your 1st level Hypothesis:
- - "In order to understand whether we should invest in Company A, I would like to check a number of the hypotheses - that the Market is Attractive, the Company is Attractive, the competition is favorable and we have good opportunities for of exit"
4) Present the main 2nd level Hypothesis:
- "In the market, I would like to make sure that the market is big enough and growing;
- In the company I would like to find additional opportunities for growth;
- In competition I would like to check that the market is fragmented enough;
- Finally, I would like to check if we have potential buyers and can achieve desired exit multiples"
Another way to use hypothesis is using the hypothesis to prioritize your analysis:
1) Make a structure: "Problem in sales may be related to Sales Motivation, Sales Strategy, Sales Coverage, and Sales Process:
2) Prioritize a part of the structure based on your knowledge / common sense / available data: "Taking into account that motivation is the core problem of the sales organization, I would like to prioritize this part of the analysis".