if it was of any concern we would have millions and millions of people all around the world totally debilitated by their covid recovery. We don't. That's why there is no serious concerns or urgency to study it. Very small proportions of people will have lasting ongoing issues, just like serious influenza cases. Sorry, nothing unique about Covid.
I think there is a misunderstanding about what is meant by long term issues. Heart muscle damage is mostly irreversible, but small damage at a young age, you will most likely not even notice it. Most of us do not use our heart to its maximum capacity in normal life unless you do very vigorous gym routines or are an athlete. As you age the small amounts of damage add up as your maximum output comes closer to your daily activities needs, this is why older pilots require stress tests, and that sadly may be the first time you find out your heart is in bad shape and your medical is pulled. Don't confuse actual heart muscle damage with coronary artery blockage, that can be fixed via stent or grafts, that's just fixing the fuel lines to the heart, if the heart muscle is damaged by the lack of blood then you lose heart capacity and generally don't get it back. Lung damage can be reversed in some cases, you can chop out a large chunk of lung and it grows back, unlike the heart, which damage can be counteracted with making other parts of the heart work harder/more efficiently, but not reversed. Yes bad cases of the flu can cause similar damage, just due to the body being over-stressed, but this heart inflammation is being found in even mild cases of covid, and asymptomatic patients.