> There is basically one editor.. Inkscape.

Do you mean in terms of open source vector editors? As there a wide variety of tools with SVG authoring/editing capability, among the most well-known being Adobe Illustrator, Sketch, Affinity Photo/Designer, even some web apps are available that were made for online SVG editing (eg: SVGator).

Inkscape, like some tools such as Affinity's, adds its own XML namespace with custom attributes and values, though for arrows I would expect it to use native `marker` elements.

It's certainly true that with SVG's flexibility and particularly with cross-browser handling differences/bugs it can become its own task to get consistent presentation when doing more complex things with it. Still very fond of the format.