Much of the flavor we expect from garlic comes from tthe sulfides present in the little veggie. The same is true of onion. Sulfer and sulfides are highly aromatic and quickly evaporate into the air when the garlic is heated. That is why the air smells so garlicy. Also, much of the flavor is dissolved into the oil. If you removed the saute'd cloves and placed them into the potatoes, you had already lost most of the flavor, leaving mostly the sugars behind.
Next time, melt the butter into your skillet, add the garlic, and cook as you originally did. But poor the melted butter and garlic into the potatoes. The flavor will be carried by the butter into the final dish.
If you look at each of the other techniques listed, the garlic was either roasted and placed whole into the potatoes, or used as an ingredient in a sauce or fat of somekind, which was used in the potatoes.
I love fresh garlic. But, if I goof up the garlic flavor by using too little, I have a standby bottle of granulated garlic that helps me correct any mistakes.
Also, garlic is very pungeant, and too much can overpower the delicate potato and butter flavor. Good mashed spuds are creamy, with a dairy flavor (my lactose intolerant sister adds non-dairy creamer to give her mashed potatoes that dairy flavor), and a bit of saltiness. More flavor depth is added by introducing onion, garlic, chives, evaporated milk, pepper, etc. Just remember, there are both sweet and savory componants to the flavor. And a great batch of smashed spuds has succesfully ballanced those flavors.
One last thing, I use yukon gold potatoes exclusively now for my mashed potatoes as they have a creamy, almost sweet flavor, and a wonderful texture. And too much fat 9butter) can make the potaotes gummy rather than creamy.
Seeeeeya; Goodweed of the North