I'd get a  boost gauge on it first.     It doesn't take much to plumb-in a  gauge to a  test port somewhere on the intake.   

people will  swear their  'turbo turns freely'... which it may!   The problem is, is  when bearings begin getting loose,  the  turbine/compressor  wheel will grind away fins/housing  as it goes.   and try as you might,   you'll never get it to  'drag'  by spinning it by hand...  as the tolerances have been  'removed'<  making it a lot less efficient.
as it gets worse or closer to imploding,   then yes,  it's quite obvious then.    


I've seen  mufflers with rusted baffles- even packed with  squirrel gathered  nuts  causing  low  boost conditions..  
So like others that mentioned,  it's not always the  turbo if you find  actual low boost pressure.