The 'flex' as you call it of a crankshaft is minimal- especially in a Polo Block, granted on A series engines of old you'll have issues, this isn't why a con-rod is allowed movement on the crank thought is it.
The real reason is to allow a clearance for the oil film to be expelled and thus have oil flow, besides the fact that engine built without endfloat is siezed solid, ergo to have endfloat you also need clearance on the rod laterally- imagine it as a self centre with the gudgeon pin (also floating).
The reason for the movment isn't to allow for 'crank flex'.