[apledger3]

Extensibility is a good way to sum it up, but there's many specific issues with each. The biggest problems we hear about with Squarespace are responsive layout overrides. The templates are also generally pretty rigid.

Wix's current editor is based on fixed position (think photoshop / illustrator). This approach works great for banners, graphics, icons etc, but is inherently at odds with web design. The solution for fixed position builders is to hardcode breakpoints, but there are too many devices. It's better to just design a UX around the box model, as that's how we code for the web anyways.

Editor X has potential but there's a little too much magic happening in the layout for my taste.

These are just a few of the many pain points. From our research, companies rarely keep using Wix / Squarespace after a certain stage. I personally haven't tried scaling a Squarespace or Wix site, but I also have never gotten them to a point where I was happy with all of the details before deciding to just code it myself.

[icameron]

Wix has a responsive layout from what I've seen as a casual maintainer of a rather large Wix site, which was originally built by a non-coder. Maybe it was part of the template he used, but a row of 3 images on Desktop automatically becomes a column of 3 images on mobile, and the top menu turns into a hamburger. You can also switch to mobile mode while editing to adjust the layout of the mobile version.

[andrewl-hn]

It's more complicated than this. You design a desktop version of the site in Wix, and it automatically generates a mobile version. Some widgets like image galleries and lists are responsive, but they have hardcoded rules.

So, it's not a fully responsive templates, but they are good enough for most websites.