Hardly a step backwards - Mac does not do what he is asking for. In fact, Finder behaves the exact same way, no folder sizes displayed in detail view. My opinion is that finder is far short of where Windows is today.( El Capitan/ Win10 Comparison being
made here). My annoyance on Mac includes the inability to grab several folders/files and get one size for them all in properties - on Windows you easily can. Try grabbing 30 folders on Mac, click "Get Info"? and the result is 30 windows popping up! lame..
Windows will sum them and tell you the combined size.
Even cooler is when working with media files (home videos for example) you can control-click just the files you want to include on an editing timeline - not the whole folder, or "select all" - and Windows will tell you the run time of the combined videos,
plus the combined size. Far better information than Mac.... and explorer is far friendlier than finder. Glad Mac finally caught up to the "Merge" folders feature which was in Windows for years.