Your doc, like most docs, is probably woefully undereducated on the subject. Or at the very least he's so used to the average patient that anything above average is just a relief.
Episodes 236-238 of the Barbell Medicine podcast goes more in depth about the health benefits of endurance training and what a good target is for health benefits.
But by not doing cardio, you're actually leaving a lot of low-hanging fruit on the table. The second slide in this video might be persuasive: https://youtu.be/ovM3mD5Roow?si=IRSRjsq8MRas9Yq6
Episodes 236-238 of the Barbell Medicine podcast goes more in depth about the health benefits of endurance training and what a good target is for health benefits.