As an anecdote of one, I was doing moderate intensity endurance exercise for a couple years with only modest improvements in basic cardiovascular metrics that kind of flatlined over time. As an experiment, I switched to high-intensity interval type training for a couple months, which required about half the time to do. All of my cardiovascular metrics immediately changed in a strongly positive way. When I did the old…
That sounds exactly like what one should do for, say, couch to 10k: build a solid base in "zone 2" (low aerobic), which also serves not just as a cardio foundation but also builds the body's ability to withstand effort and impact. Then once the base is built, to make any progress one needs stronger, more focused stimulus, so you introduce interval training at high aerobic (tempo and threshold paces) as well as anaero…
There are plenty of online training program generators that are pretty good and will take you from zero to running 10k. I used an online program to run my first 10k somewhere circa 1990.
There a lot of more cutting edge science online (and I follow Nick as well) but if you're not a competitive athlete and are just trying to get in better shape then the answer is mostly just do it. Over some base of running you can throw in some interval training including HIIT.