Looking at your the picture, the bunch you are holding is a perfectly acceptable size for an albeit smaller variety.
The large commercial grapes you get at the supermarket/market stall have often come from vines that have been girdled or treated with gibberellin to increase berry size, uniformity etc.
It may be worth remembering that the pips and skins have much of the grape's nutrition.
So eat, juice, or wine the choice is yours. There are plenty of naturally large bunched grape varieties for both undercover and outside.
Grapes are such a worthwhile crop to grow. Says someone with over 40 vines.