Referenced data is published as a Map Service or Map Image Layer, depdning on preferred terminology. It uses an older publishing technology that uses ArcSOC.exes on the server. Each uses memory and has a compute footprint. All of that means that architecturally you can only scale so far, i.e. deliver a finite number of map services. You can make those map services into feature services for editing, but you use even more memory etc. If you're using Dedicated Service Instances then ~100 is the arbitraty max number of services from a single ArcGIS Server Site. If you use Shared Instances then you can have hundreds of services.
Hosted Feature Layers can only be provided from a base deployment of ArcGIS Enterprise, it needs the Portal, Hosting Server and Data Store. Put them together and you have a lightwweight architectural paradigm that could allow you to stand up 10,000's of individual services. However, you're presenting data not maps, subtle but important difference.
Also some functions inside of a Portal (analytics/Insights) use Hosted Feature Layers as temporary storage.
Basically, if you want to use Enterprise, you need a Data Store. It's down to you how you publish.
In summary, Hosted Feature Layers from the Data Store scale better.
Scott Tansley
https://www.linkedin.com/in/scotttansley/