Every step taken, whether mistake or true, made me what I am today.  The past has a far greater influence on us than we are aware or would be comfortable admitting.  I look at my script header telling people who wrote the script, when and for what purpose.  COBOL identification division.  I've never written a line of COBOL and some of the people I work with probably haven't heard of COBOL but still the practice persists. 
Bash has been added to Windows 10.  Ancient, but very powerful.  As far as I can tell a key difference between Powershell and Bash is that Powershell handles & returns objects where as Bash handles and returns text streams.  Knowing when object handling is required or when text stream handling is required will tell you which tool is appropriate for the problem you are trying to solve.
In fact I don't worry about whether something is "old", I worry about whether it is obsolete which is something different entirely.  The great challenge of our lives is moving with the times rather than the fashions.
Steve has often commented on the expert beginner.  I have found that learning a tool thoroughly helps me understand what the inventors were intending, the fundamental principles they were applying and whether they were right to do so.  Understanding fundamental principles will help you spot the inflatable dartboard solutions and those that you can build on or contain a good idea that can be applied elsewhere.
I'm not a fan of SSIS.  I've used 5 other ETL tools and prefer all but one of them.  But too many of them aren't used primarily for ETL or even ELT.  They are used for job orchestration because OnSuccess, OnFail & OnComplete flows are incredibly useful.
I'd say that learning & understanding the principles of something is more important than learning the thing itself.  I have also found that learning about the tech surrounding your core competency makes you much stronger in your core competency.