Here's the results of a quick experiment I did recently with Lactose, Dextrin and table sugar.
The rule was that table sugar, which was the sweetest of all, worth 100 points. We then compared the other two with table sugar. I mixed each ingredient with same amount of water. Can't remember but something around 4oz.
I got my wife and kid to help tasting the samples
Basically, dextrin tastes nothing, lactose taste a little sweet, but much less than table sugar.
Also interesting is that lactose sweetness is diferent than table sugar. I have no words to explain but lactose is a cold sweetness and table sugar is warm .