To answer more directly to your question...

The API 650 frangibility condition is not considered directly as p_failure_roof< p_uplift.
Of course, you can do it in this way- however there is the risk that your Client/ his Consultant to say this is a non-API approach.

F.5.1 is a condition that evaluates the total required compression area at the roof-to-shell junction when the maximum design pressure has already been established. There "required" word would mean "required for safety operations" and you can understand from my previous post that there is a safety factor of 1.6.

I have to recognize that it is not so evident that the condition in 5.10.2.6 (which is "All members in the region of the roof-to-shell joint, including insulation rings, are considered as contributing to the roof-to shell joint cross-sectional area (A) and this area is less than the limit shown....") is the condition that the roof will fail before failure occurs in the tank shell joints or the shell-to-bottom joint.

The background of this formula is the fact the roof force can be separated into vertical and radial components. The radial component leads to the "compression" force in "compression ring". The vertical component is an uplift force for the shell.
At roof failure (corresponding to pf pressure and Fy stress in compression ring), the forces components are radial Hf and vertical Vf .
Vf< DLS (dead load of shell) means "no uplift" condition.
This condition would be interpreted as when the roof fails, this is before uplift.
The condition above written is equivalent with inequality areas required by 5.10.2.6 Frangible Roof.

Best regards.