Unless you have the gavaskars, tendulkars, Richards, laras, sobers etc of the game, it's always a matter of odds which are even or thereabouts even talking of batsmen even from the 2nd/3rd tier. Would a Smith be more reliable? Definitely. Doesn't mean he's somehow certain to give the team a good start though especially when you consider the quality of bowling attacks in the draft atm.I admit that, and you don't want that 50-50 scenario from a key batsman who needs to perform to give you that advantage you gained by winning the toss in such a tough game. There's nothing to defend Sehwag's lack of reliability, specially relatively.
Sehwag definitely isn't someone you want to rely on due to his style but harshad's batting has the likes of dravid and Pollock to follow. I don't see it as a case of Sehwag performs = draw, fails = loss either as you say in the above post. He's just 1 wheel. I'd actually call dravid and Pollock as the key to the result from harshad's batting side there, not Sehwag.