There is no such distinction between ACA, employer provided plans, and individual plans available prior to the ACA. There are tens of thousands of different employer plans in the US, because most insurers design plan offerings specific to employers. Some have broad networks and others are very restricted. Over the past decade, insurer / employer plans became more restrictive as a way to offset rising costs.
The breadth and depth of an insurance network has nothing to do with the ACA. It is the preferred method insurers use to design and offer lower cost policies, because network design is opaque, very difficult to analyze and compare. Even now, there is no discussion of network design for employer plans, yet this is as much a problem for consumers. It is not possible to compare networks, even when looking at different policies from the same insurer, because insurers do not make that information public. They only have a tool to search for a service provider because it is required, and it usually is cumbersome.
Some insurers in some states offer limited network plans. BCBS Texas is a good example. Other insurers in other states offer the same broad network plans used by large groups. BCBS Florida is an example. This is not because of the ACA, it reflects the effort by the state insurance regulator to maximize options for consumers.