Subsites in SharePoint are not going away any time soon. However, creating every site as a site collection, using Hub Sites to group them together is the recommendation for the future. This results in a much flatter hierarchy.
All of the latest innovations around branding, provisioning, information architecture, and security, are geared towards this site collection approach.
Read more here: http://bit.ly/2s1lm89.
Posted by Eric Gregorich, Sr. Solutions Architect