I would actually suggest arrows to be a special case of lines (I've submitted a proposal for a line tool at https://feedback.okso.app/feedback/p/line-tool), and in both cases they should be "curvable".

Following Okso's intuitive interaction model, I would suggest something very natural, manipulating points directly in the curve, instead of controlling Bézier handles. Something similar to Inkscape's interaction mode when dragging a curve with the path tool, especially when the nodes are set to auto-smooth, would be ideal IMO.