The same amt of def lvl when used on barb is more op than when it is used on other classes. Similarly, the same amt of att lvl when used on wizzy is always more op than when it is used on ep or bm. The point is you cannot compare things on an absolutely naive basis. There are many factors that can affect the overall effect of the same thing.
The value of 25 def lvl on a barb >>>>>>>>>>> the value of 25 def lvl on an ea. Why? because def lvl combined with barb's high def will be even more op, needless to say.