Three summer internships is roughly a year of industry experience, especially if they are done at 2 (but not 3) different companies.

Actually, those three 3 month engagements can constitute several years worth of experience if they are done with excellent mentors at good companies. Reasons:

1. You see several teams, several projects, several codebases, without having to spend an awesome amount of time at one place. How many engineers work with multiple teams and companies in their first year (without one of those experiences being terribly catastrophic)?

2. You get the interesting meaty projects, or get to work on prototyping projects, but are also expected to contribute to the existing code base (or at least build on top of it). You participate in meetings, give presentations, etc. Basically, you see an entire compressed project/product lifecycle but embedded in an existing codebase.

3. Most importantly: Doing 1 repeat internship is super valuable. Spending 6 months at a place in 3 month increments with 9 months in between is an exceptionally unique experience in terms of understanding how orgs work and evolve. Most engineers don't get to experience until they are in the consulting portion of their careers.

University students in CS should do as many internships as possible, and universities should be more proactive about finding a way to mock summer internship experiences for students who do not get any internship offers.