The thing with recommendations of 2.5 hours a week of 5 fruits and veg, etc. is that it is a generalized suggestion for the majority of the given population, that should lead in an average of ideal health. It is not meant for children, the elderly, those with diseases, or others beyond the main population.
Anyone who monitors their health or looks more in depth at the actual mechanics as well as their own situation can fine tune things a lot better, and in the end it mostly comes down to how it makes your body feel and act (though some will be hidden so knowing the mechanisms helps).
Exercising at different intensities and durations has different effects on the body, higher intensities raises heart rates even higher, increases the ability of the heart to make beneficial adaptations in efficiency and health, and increases metabolism by more than lower intensity exercise, and increases it for longer after the workout. It also increases insulin sensitivity to a greater degree, being a big boon to those T2's out there.
There are a host of other benefits at different intensity levels and durations, which each will use different amounts or percentages of the 4 human energy systems, so they all play a part in working out. For diabetics and people with weight/metabolism/heart disease or risk thereof, high intensity can be a great tool if appropriate for your health, it isn't a matter of short circuiting or risking your body or health, though I will say that any degree of intensity should be cleared with a professional, especially high intensity as some people's body's just aren't in a position for that yet, due to illness or medication. There is nothing inherently wrong with high intensity exercises, however.