Skype was not alone, as WhatsApp was also accused of being a battery killer, at least at some stage of its pre Facebook-acquisition life. Most messaging apps tent to drain your battery faster than you would want them to. To achieve these savings Microsoft has turned off push notifications on group chat messages. That is how Microsoft can "leave Skype running all day with no noticeable battery drain."
If you really need these notifications you can turn them back in Settings > Notifications > Sync group messages and they will be back, but this will hurt your battery life. There is still a huge gap that needs to be bridged between Skype for x86 notebooks /desktops and Skype for Android, as the latter still lags behind the firstborn x86 version in overall performance and user experience.
Like most consumers we use both, but since Microsoft is the owner of the application, it will probably run it better in Windows of any sort, rather than on Google's Android or other operating systems.