You can look at the Forrester and Gartner of this world, but for a less subjective and more objective metric you can look at the statistics related to the CMS used by high traffic website [0]. I won't even say Wix, Squarespace, Joomla (is this still a thing?) or Shopify are in the same category of AEM, they missed a lot of the qualification criteria to be considered an enterprise level CMS.
Wix, Squarespace, and Shopify are Tier 3 CMSs at best.
Drupal, (managed) WordPress, Joomla, Cake, Webflow etc. are Tier2.
AEM, Sitecore, BloomReach, Contentful, Contentstack, etc. are Tier 1
The CMS ecosystem is further segmented into products that are headless, decoupled, hybrid, and monolithic. To complicate things, there is a new type of product called DXP (Digital Experience Platform), which mixes in marketing systems into the stack.
