WordPress is extensible. What does that really mean? WordPress can grow well with a growing company and is a good base for that. There are a lot of plugins available for wordpress that add capabilities with nuances that go beyond that make it more customizable than Squarespace or Wix or Weebly or Websitebuilder.com.
These are also each hosted solutions so it can’t be used with the hosting through Fascination Design.
Also if you hire someone who solely works with Squarespace or Wix they may not know how to code and have a world view more limited to those platforms. I’m not a fan of Wix but Squarespace isn’t bad. If you want to DIY because you have more time than money then it would be a good choice.
Fascination Design does not build sites using squarespace etc. because it doesn’t give us the level of control and customization capabilities that we’re used to. I also do NOT offer support for the site options mentioned above so if you get started there and run into a problem, you must work with their customer support.
So it’s your choice, long term scalability or DIY.