Hi Matuz. Most store bought fruit is (sadly) harvested long before the point of peak ripeness so it is (in my opinion) always better to look for fruit from farmers markets or to grow your own. Many people making "country wines" tend to use 3-5 lbs of fruit /gallon of wine and use water to make up for the missing volume. With some fruits, their flavor-rich juice, permits this. With other, less flavor-intense fruits (peaches and strawberries and the like) diluting with water does not make for a flavor-rich wine. That said, the amount of sugar you are going to obtain from fruit is on a par with a cider or beer (starting gravity of about 1.045- 1.055) , so you are talking about a "wine" at around 6 -7% ABV. Two possible solutions to increase the fermentable sugar: a) you add sugar (and if you are diluting the juice with water the starting gravity will drop so you will need to add more sugar) or b) you freeze concentrate the juice and you then collect the first runnings of juice as it slowly thaws. The first 1/3 of the juice that thaws will have almost 100 % of the flavor and sugar. But that suggests that you need 3 gallons to make a single gallon. Not inexpensive.
There is a different approach and it is one that I often use when I make a fruit wine (my preference is to make wines from flowers , eg elederflower wine or wines from honey, ie mead) is to use fruit juice already bottled and in my supermarket's chiller section. The juice is very rich in flavor and contains nothing but the juice. The downside is that you don't get any of the complexity of flavors from skins and peel, though there is nothing to prevent you from adding some to your primary.