Different sugars have different relative sweetness (in %) (Elmhurst College):
- Sucrose: 100
- Fructose: 140
- High fructose corn syrup (HFCS): 120-160
- Glucose: 70-80
- Lactose: 20
Relative sweetness of some non-sugar sweeteners (NutrientsReview):
- Aspartame: 180
- Acesulfam potassium: 200 (in some diet colas)
- Stevia: 300
- Saccharin: 400
- Sucralose: 600
Plain yogurt (100 g) contains 4.7 g sugars, but mostly lactose, which is not sweet. (NutritionData, milk composition)
I don't know, which sugar is in Kirkland Protein Bars, but if it is HFCS contains stevia (300% sweetness) (link - read at the bottom of the Nutrition Facts), therewhich explains its sweetness. Stevia is a reason why 1 g of it tastes quite sweetnatural non-sugar sweetener.
Perceived sweetness can increase with the food temperature (ScienceDirect) and salt content (a study in mice). Liquid and solid foods with the same sugar content can have different perceived sweetness (ScienceDirect). And there are sweet taste enhancers...(ChemistryWorld)