HOI3 always showed the number from the attacker's perspective: 60 apparently means that the attacker is inflicting more damage than the defender, not necessarily that they are 60% of the way to winning. If you're being attacked in HOI3, you want to see low and steadily decreasing numbers, meaning that the attack is failing. If you're attacking, you want to see high and increasing numbers. The direction of the attack icon mattered. It looks like HOI4 is showing the number from the player's perspective now, which is probably an improvement, so high numbers are ALWAYS a good thing. Either way, it still appears that INCREASING numbers are the best sign that you're winning, more than the absolute number.
I recall several battles where I swamped a province on the Maginot Line with attacks from 3 directions and multiple units from each (including ENG in several of those divisions). The attack progress bar initially showed only around 14, which steadily rose to 100, at which time the defending unit ran out of ORG and retreated. Total casualties over the course of the entire battle were roughly equal. That may mean that my units were initially inflicting only 14% of the total casualties, and suffering 86%, but each of my individual divisions was taking far less casualties than the defender. As the fight continued and the opponent ground down, my units began inflicting more casualties than the defender. It may mean that It judged my "progress" at 14%, based on some unknown formula. It may mean something else, but I haven't seen anything to say specifically what the numbers represent.
A little clarification would be appreciated.