The new design/architecture allows them to do great stuff in the name of efficiency; for example, when browsing through some parts of the UI, it's now much more capable of just updating the part of the page that's changed, rather than having to reload the entire thing. This is a significantly better approach for a lot of things.

I understand that the 'updating the part of the page that's changed' functionality is now dramatically slower, more unresponsive, and less reliable than the 'reload the entire thing' approach was, and it feels like browsing the site via Citrix over dial-up half the time, but look, sacrifices have to be made in the name of making things better even if the sacrifice is that things get worse instead.