There may be some misconceptions here. The amount of oil in the crankcase or sump has *no* relation to whether that engine was overheated or underlubricated. As long as there is a sufficient supply of oil to the pump to ensure proper oil pressure, then everything is cool, no pun intended. Having excess oil in the sump gives you no benefit other than to keep the oil pump supplies as oil gets consumed.
Neither is black oil a sign of anything dire. Between oil changes, piston engine oil can get quite black, especially as the engine accumulates time toward overhaul. In a worst-case scenario, the engine in the original post may have high total-time and coincidentally be coming up on a scheduled oil change. It would not necessarily be cause for concern to me.
Then too, some engines can burn quite a lot of oil and still be within "specs." I forget whether it's Lycoming or Continental that doesn't even publish a maximum consumption limit. So it's conceivable that the previous pilot had an adequate supply when he took off. What was the length of the previous flight period? When was oil last added to the engine?
We all like to have our self-righteous rants, especially when we can point out the failings of other pilots. But truly and simply, this is why we do preflight inspections. You cannot say, "I'm glad I did!" about a preflight; it is your responsibility and duty and is not optional. There is a reason we do post-flight inspections too. If you're not doing it, checking the oil after you land is a smart idea.
The aircraft is very likely not an unairworthy timebomb. Or maybe it is, if it has that much blow-by and a very high consumption. Don't freak out over it, just bring the oil up to the proper level for your flight and make a note in the maintenance log of the amount added. Have a calm word with the head guy of the outfit and move on.