During this years, some legacy components of the vSphere suite has been dropped, starting from removing (in vSphere 5.0) VCB, Converter Enterprise, Guided Consolidation, and the historical ESX Server. The latest removal was the TPS memory management (in vSphere 5.5 with latest patches).
In those year the old vSphere Client (the Windows client side) has been deprecated (from vSphere 5.1) and all new features and functions has been introduced only in the vSphere Web Client that is a web oriented client, multi browser and multi platform.
But for several operational tasks and for all the legacy vCenter plugin, the old vSphere Client was still necessary, and of course was necessary to manage a single ESXi host without having vCenter Server (the server part of the vSphere Web Client is a vCenter component). Also there were some limits in the Web Client.