Who's even making this argument, though? Nobody is claiming that having x star player is an unequivocal guarantee of success, nor were they back in the heyday of C9 TenZ when there was a strong consensus that he was the best player in the region.
Comparing star players is, if anything, implicitly making an argument about these nebulous 'other factors' - namely the degree to which any shortcomings in that area might be bandaged over by the miracle X factor that certain players seem to regularly bring. Similarly, having a top star player provides a nice hedge against the unavoidably random nature of Valorant games where any matchup is ultimately a coinflip, albeit one of wildly varying weights.