I can see I am fighting a hopelessly losing battle in the like-war against "PEWSian CW orthodoxy"
, but....
actually yes, that would work (assuming the player's cunning ploy didn't become public knowledge, in which case I would surely hold it against him) if the player had a long career. If he had a relatively short career I would adjust my rating accordingly. It would work because in reality we can't make assumptions about whether the player "wasn't good enough to play test cricket until he was amazing at it" or whether the player was just actually really amazing at test cricket. We can't make assumptions about whether a player was about to decline horribly as soon as he retired, or whether he just retired at what seemed a suitable time (because you can't and are not obliged to play test cricket your whole life).
Your (evidently very popular) opinion at once eschews assumptions, but then seemingly relies on assumptions to rate the Tendulkar-type over the Sanga-type. You have to assume that the player who has big slumps in his career has slumped because he has heroically played on for the good of his team, and you have to assume that the player who doesn't slump avoided the slumps due to quirks of selection or a canny retirement, and not just because he is amazing- and yet typically the only evidence that actually exists is "that guy was amazing". "The bastard avoided an inevitable form slump by retiring at the youthful age of 37" is pure speculation.