I've made blackberry wine a few times now - after some experimenting I've settled on 6 lb fruit per gallon which makes a really nice dry wine with no additional acid or tannin.
The seeds or skins of the Himalayan blackberries that grow wild seem to have a lot of tannin. Last year I made 2 batches - one with the pulp removed after 6 days and one with the pulp removed after 4 days, and the latter one tastes better to us. That's with the berries frozen and thawed, and the pulp bag squeezed well.
I generally use 5-6 lb of fruit per gallon for fruit wines, as do lots of people, and the resulting wines don't taste "diluted" or "thin" to me - but everyone's taste is different.