Well rounded means often not focused because, only top notch developers really grasp more skills efficiently.

Average developer will mix up everything and won't be able to work without google search. Don't spend much time with learning JavaScript. Every monkey now learns JS and do you know why ? because it's dead easy. JS leads to Front-end development and that's often pain in the ass.

I vote for solid knowledge of SQL, Java and maybe Python or Ruby but don't learn everything in one time. Step by step e.g. each year one new technology or language.