Let's slow down and clarify few things. Even if your school has a committee letter, you are no way "required" to use the letter. That sounds like if you don't use the committee letter, your app gets thrown in the trash, which is certainly not true because there are numerous applicants here on SDN and elsewhere that ditched the committee letter and stuck with Interfolio. Results? Schools didn't care, and the applicants received several acceptances.
Committees have only one purpose. To help the adcoms by summarizing the contents of the letters from professors/PIs/coordinators etc. who do know the applicants personally. After all, adcoms don't want to be overwhelmed with numerous letters from each applicant.
Yet committees are incredibly flawed and manipulative. Several committees charge a fee to hapless applicants to receive a letter. Other committees require extensive interviews and provide very vague and often lukewarm evaluations, which tank the merit of the applicants' otherwise solid application.
Think about it this way. Would you want a letter from someone who knows you very well, or from the committee who hardly knows you and makes a living by taking advantage of hapless applicants?