The shrub flopping above.

This is a mature Coppertina ninebark. Arching branches are part of the charm if you allow them space to arch.

Same as with non dwarf kinds of forsythia, spring blooming spireas, Kolkwitzia > Linnaea, Abelia > Linnaea and weigelas - the fountain like habit is a big part of their beauty. So that cutting or shearing them back into balls or worse does much to defeat their purpose as decorative features. As does selection of genetically dwarf versions that grow as short branched tufts or mounds.

"Arching branches are part of the charm if you allow them space to arch."

Exactly! We've got an older Diablo, which lists spread at 4'-8'. I agree with that, if you're willing to prune off older arching branches. Otherwise, if you want to see it arch & spread to its capacity, give it 10'-12'.

Most ninebarks are very large shrubs. The shrub the OP shows is crammed up against the fence.

Thank you for all your responses! We initially thought of removing it but seeing that it is meant to have arching branches, we decided to let it be and see how it grows in the following years. We will make a pretty garden around it.

Cant tell where you live but they usually get mildew. Be on the lookout for it or your shrub will be white, wilted and slimy in short notice. People swear by spraying a solution of 1 part any-kind-of milk and 10 parts water preventively. How will you know? When you see a few leaves with mildew you're just a little late! Spray away.

As time goes on you'll learn what's "preventive" timing and what's 'opps just missed the window" timing.

I have 5 ninebarks, 2 Diablos, 1 Coppertina, 1 Summer Wine, and 1 Lady in Red. Mine have never gotten mildew--not in 15 years, hot summer, dry summer, wet summer. No mildew.

Summer wine is a keeper. Prune it the way you want it to look; after flowering if you like the flowers or anytime if flowers aren’t a concern.