Your lawyer is only half right. You are exempt from the excessive demand criteria for inadmissibility (costing health care too much). However a family class applicant could be deemed inadmissible for the public health and safety criteria.
If you have questionable results in your medical test, CIC will demand you take additional tests to clear things up. So it's better to do all required tests now before submitting your application to ensure the VO sees a clean bill of health with no questions, rather than wait for CIC to contact you later and further delay your processing. Having to re-do some medicals during the processing can add months to your time.