The Big Thing about the mortgage valuation report is that it is for the benefit of the lender, not the buyer.
The lender needs to know that it will be able to recover the value of its loan and associated expenses if it has to repossess the property in a hurry.
It isn't concerned to ensure that the buyer is getting a sound investment or that the property doesn't need remedial work doing to it. This is a "how-well-do-you-sleep-at-night?" point: the buyer has to weigh the additional cost of a survey against the risk that the property isn't in sound shape and will substantial repair or other works.