That... doesn't sound like HIIT. HIIT shouldn't average out to anaerobic heart rate ranges, otherwise you really lose the benefit of keeping your heart engaged in aerobic ranges during the rests. And to be honest, HIIT used for recreation shouldn't even peak in the elevated ranges above 167 bpm, if you're talking about doing it safely over years for health. Higher than that might be effective in training to increase aerobic capacity or lower your overall heart rate, but may damage your heart over time.
The effect of taking those controls on HIIT should result in reducing the autonomic stress response of /all/ exercise on heart rate, not increasing it. The demonstrated effect of HIIT is being able to efficiently scale aerobic capacity without increasing the time required and prolonged physical stress on the body. That's why Olympic athletes have been using interval training for a century, and from the 90s to this day, have used HIIT techniques like Tabata to increase their overall ability to exercise for a long duration, without having to actually commit to exercising for repeated long durations.
I'm not sure where you got that piece of information about loads of people with great anaerobic "metabolism" vs aerobic "metabolism". It would truly be very difficult, but not impossible to consistently raise your anaerobic capacity, (which I'm guessing is the implied relation to processing lactic acid efficiently as a fuel source for exercise?) but not raise your aerobic capacity also. Most of the ways I have seen that involve some kind of ketosis, or something that would otherwise deprive the body of the baseline glucose to drive aerobic capacity up in tandem with anaerobic capacity (because there's just not available excess glucose to store as glycogen in muscles beyond basal mechanical muscle operation and may lead to atrophy from burning muscle as a fuel source a.k.a. awful orange piss). And generally you would have a hard time building up extra muscle in that state as well, so it would be generally not advisable/possibly extremely dangerous to do so without proper diet and nutrition.
disclaimer - I am not an exercise physiologist or certified in any way. I'm an idiot on the internet, so please feel free to correct me if I'm wrong or don't have it quite right
The effect of taking those controls on HIIT should result in reducing the autonomic stress response of /all/ exercise on heart rate, not increasing it. The demonstrated effect of HIIT is being able to efficiently scale aerobic capacity without increasing the time required and prolonged physical stress on the body. That's why Olympic athletes have been using interval training for a century, and from the 90s to this day, have used HIIT techniques like Tabata to increase their overall ability to exercise for a long duration, without having to actually commit to exercising for repeated long durations.
I'm not sure where you got that piece of information about loads of people with great anaerobic "metabolism" vs aerobic "metabolism". It would truly be very difficult, but not impossible to consistently raise your anaerobic capacity, (which I'm guessing is the implied relation to processing lactic acid efficiently as a fuel source for exercise?) but not raise your aerobic capacity also. Most of the ways I have seen that involve some kind of ketosis, or something that would otherwise deprive the body of the baseline glucose to drive aerobic capacity up in tandem with anaerobic capacity (because there's just not available excess glucose to store as glycogen in muscles beyond basal mechanical muscle operation and may lead to atrophy from burning muscle as a fuel source a.k.a. awful orange piss). And generally you would have a hard time building up extra muscle in that state as well, so it would be generally not advisable/possibly extremely dangerous to do so without proper diet and nutrition.
disclaimer - I am not an exercise physiologist or certified in any way. I'm an idiot on the internet, so please feel free to correct me if I'm wrong or don't have it quite right