I understand the rule perfectly fine. Note that there is also a cost cap in place that was not there when power unit penalties were first introduced.
All teams aim to be reliable. I doubt Ferrari were searching for some magic performance advantage with Leclerc's control electrics, Sainz's seem to be just fine. But they failed, and now he has a penalty for something that broke and caused a DNF. It just robs the fans of a battle at the front.
If you blow more than your allocation of engines for the year - they will be replaced anyway. Look at last year, for instance HAAS used 11 ICEs for the year, their allocation was 6! Renault used 12. Let them replace them, it just means they can't spend on other things such as aero upgrades.