Inkscape is a lot more versatile than Affinity Designer. So it all depends what you need to do. But also how you like to or are used to work.
Inkscape is more of a CorelDRAW than an Illustrator clone. People who come from CorelDRAW, like me, usually disrelish the way curves are edited in Adobe products.
As much as I like Affinity products (I own both Photo & Publisher), I prefer Inkscape any day over Designer (or Illustrator) for this reason.
The other reason I simply couldn't use Designer at all until approx. six months ago was that is lacked snapping of curve handles to grid intersections. It took Affinity years to implement this essential feature for people who do typography or logotypes[1].
As others mentioned: the Carbon native Inkscape (beta and now release) are even slower than the XQuartz version. Which was already slow, compared to running Inkscape on Linux on the same MBP.
For this reason I now use Vectornator[2] (free) as much as I can. For the missing bits I go back and forth with Inkscape.
Not ideal but it's only recent that the macOS version of Inkscape has seen more love from the developers. I hope that soon performance will improve and I can do everything in one app.
[1] https://forum.affinity.serif.com/index.php?/topic/38389-feat...
[2] https://www.vectornator.io/