I would have thought if the design didnt have to accommodate small radius, then more reliable running should result, not less.
Wide tolerances, in manufacturing terms, does not mean a good end product.
Being able to narrow down what the chassis has to do should enable a better design.
But i am not sure there is a link as Kato has proven that tight curves AND high reliability can be done.
even though I agree with you that narrowing down what a chassis has to do CAN lead to better design, it can also be used to make a cheaper design, which is where the tollerance issue comes in, that is to say the model is only able to do what it is designed to do, and if it can only just about do that, then only a small window of functionality is inbuilt.
Kato doesnt recomend the long passenger trains to go narrower than 315, but they can (i imagine the reason Kato recomend 315 is because their track spacing is rather narrow and 315 may well be desired to stop passing trains hitting each other). So perhaps having a wide tollerance does have an impact on the quality of the product.
Kato could have said to themselves "our trains will hit each other if they pass at radii less than 315, so we'll design them not to be able to and because the design brief is more specific we will therefore produce a better model" , i'm sure being a business they would dearly love to, but one read of the sentence shows the paradox.