You raise some good questions.
I read the article from St. Lukes and it is not clear if those statistics are for their hospital, nationwide, or some other hospital.
The death rates, and especially the rates for a 3.5 cm aneurism, seem disproportionately HIGH when compared with the numbers for larger aneurisms. Personally, I do not understand how/why the risks at 3.5 cm would be greater than the risks at 4.0 and/or 5.0 cm
That said, it is also clear that once an aneurism is larger than 3.5 cm, the Risk of a Morbid Event or Mortality is Greater than ZERO and the difference between 4mm and 5mm is not all that great. The recommendation for waiting until 5.0 or 5.5 cm is based on an (OLD) assessment of Surgical Risk.
Once again, the Better the Surgeon, the Lower the Surgical Risk and the Lower the 'crossover' between Surgical Risk and Risk of an adverse event with the aneurism.
Bottom Line: (IMO) Surgery for an Aortic Aneurism follows the VR.com mantra about surgery for Bad Valves, i.e., SOONER is BETTER.
This is my very NON-Professional Opinion.