By that logic, one might be 'naughty enough' to suggest that whatever changed Sachin Tendulkar in the mid 90s is what made him the great batsman we know and without that change, he may have been another ordinary batsman ( very ordinary indeed from the suggestion of those first few years of his caeer).
His numbers early-on were still fantastic and I don't think there was any doubt he'd be a great. I have footage of his 148* at the SCG and it, for a seasoned Test player let alone a 19-year-old bloke, was masterful. The 114 he scored at the WACA was a great counter-punch knock too. Both knocks were studies in batsmanship; the 148* had every shot and was a highly orthodox knock. The 114 was a time where his side was in trouble and his ability to improvise in conditions which would have been completeley foreign to him came to the fore.
His record after that knock was 16 matches, 951 runs, 3 100's, 4 50's, ave 43.22. After a subsequently ordinary series against SA, he biffed the daylights out of Zim and from there onwards, his average rarely dipped sub-50. My personal opinion was that what changed him was his greater propensity to knock the ball into the stands. Early-on, he was an extremely orthodox player who had an uncanny knack for hitting the holes in the field. It was when he started hitting well over the fence that I thought he became a world-beater. I'm pretty sure consistent success as an opener in ODI's was responsible in-part for this too.
As for Murali, I think that around 1998 he started to not rely so heavily on just ripping the ball and using his head a lot more. Since then, his numbers speak for themselves, really. And, if anything, I say his introduction of the doosra has resulted in a lesser bowler. Against guys who were new to it, it was a potent weapon. Now people are used to it, I'm definitely in the camp who says he over-uses it. It must be hard not to if you can turn a doosra more than most leggies can turn the ball but, as was shown in the Super Test, his orthodoxy as an off-spinner makes him great. THAT spell was, well, wicked.