Your assertion is there is no difference in value between off an on target shots. What you then proceed to do is provide an edge case scenario. Would you agree, that in expectation (on average), on target shots are more valuable than off target shots. Because the vast majority of off-target shots aren't "ones skyrocketed from in front of an empty net".
Notice how this relates to my above point. Too arrogant, not critical thinking enough.
Let's talk seriously then:
The area you are touching is related to all the Xstatistics. The fundamental principle of calculating xG (which is the stat that measures by definition the value of the shot) is that it doesn't take into consideration where the shot ended.
Factors that most models use in their calculations are: - locations of the shot, distance from goal, players in between the ball and the GK, positioning of the GK, speed of the ball the moment of shot, positioning of the body of the shooter, etc. And many others, the models are becoming increasingly sophisticated.
The statistical methodological assumptions you mention are all in there, and vary from model to model. Of course, no model is perfect.
The expectations of a shot becoming a goal has to do with all the above, which are all PRIOR to the action. The end result of a shot, on the contrary, occurs AFTER the action. This means that it doesn't yield 'expectation'...
Now, what you are possibly trying to insinuate is that the end result of a shot can indicate a backwards correlation with scoring a goal, a 'reverse' expectation so to speak. There might be a correlation there, that's why people thought in the past the on/off target stat is important and were reporting it.
However, that would be substantially weaker than the correlation between G and xG, which is forward-oriented correlation. It looks at anterior conditions that statistically lead to a goal, instead of trying to statistically hypothesize from posterior conditions. Just as with any kind of backwards causality, backwards correlation is in a way putting the cart before the horse.
Data science in football has moved the last 10 years towards xStats for such reasons, and totally away from looking at end result stats (goals, assists, wins, points, etc), let alone stats that can only vaguely be backwards-correlated to the target end results stats (like on/off target or possesion), which was the norm 40 years back for instance.
PS: If you are actually doing data science in your real life, it is surprising that you don't take the xStats more seriously than you seem to take them in all the threads here. People working in football data science, are employing the same tools that you do in a different field
PS2: It's funny that many of you accuse me of arrogance, because I hold and defend my views. Usually I have an argument for that, I don't do it because of any fetish. And usually I do not change views easily, because the argument I have seems to be stronger than opposing arguments.
On the contrary, I see the exact same people accusing me of arrogance being super arrogant in their own views, even when these views are less well-founded and less backed by arguments, but more backed by consensus of the majority.