This first chance thing is an interesting way of looking at the world.
But...
If you depend on a simplistic formula -- "the failures of the opposition should not be taken into consideration, the chance should have been taken, all chances should be seen as out" (which is what I understand the first-chance thing to imply) -- then you have to also include other factors.
For example, a more skilled captain might have set different fields, so things that aren't even seen as chances would've been chances if a fielder had been in the right position. Therefore the runs shouldn't count to the batsman's name.
Or, a better bowler would have got the batsman out earlier; the fact the batsman was able to score so many runs is not due to his own ability as much as the failure of the opposition to bowl better, or the failure of the opposition captain to rotate his bowlers appropriately. Therefore the runs shouldn't count to the batsman's name.
I'm sure there are many, many more.
The point is, the weaknesses of the opposition -- whether in terms of dropping chances, setting fields, bowling better, better captaincy -- are integral to not only the figures the batsman produces but also to the way he plays the game. It is his knowledge of this that in part determines his success. Sehwag is an example -- he knows he can get away with more than some others do because of the way he plays his game. Viv Richards was another -- he was so intimidating that captains set fields for him they would not otherwise have set.
So I reckon the first-chance business, while worth passing attention as a view on the game, is ultimately not worth a lot. Every batsman plays the opposition he faces, not a perfect opposition; and the knowledge the opposition is less than perfect is integral to the batsman's approach to his innings.
Surviving chances is not always luck; it may be down to intimidation, aggression, calculation...
Anyway, that's my 2 cents