I think the problem is when people use MBTI to do too much. A few things it is not are skill sets or even preferences for activities. Look at the title of Jung's book: Psychological Types. It's about different mindsets, which we recognize as a significant part of "personality". It's basically the way a person prefers to think about stuff. That means Ss & Ns may notice & think about the same stuff, but they prefer to do it in different ways. It's not about noticing or not noticing details, its about how they are noticed (in the mind I mean). Examples: The focus of the iNtuitive is usually not the literal detail in its own context. The detail is harped on as an extension of something else (an idea, a concept, etc), which can certainly seem pedantic, nitpicky, stuck on semantics, etc. The focus of the sensor can be big picture when placing ideas in the context of reality. The details are just unimportant crap getting in the way then, as they have no significant impact on what is real. And of course this is not about ability - it's about automatic preference for the way you think about stuff.
MBTI is just identifying & categorizing intangible differences in the way people think. It's hard to do because its not concrete - agreeing on exactly how to define these differences is rough when you're groping in the dark & possibly touching on entirely different facets of personality. Jung presented a framework that rings true to many. We "see" these types all around us, we see ourselves in them, but we also recognize they are vague sketches, not complete pictures by a long shot. At best it helps us understand that others think differently, and one way is not more valid than another.
Of course, there are patterns among people who are the same type. If a person prefers a certain thought process, then they are likely to seek contexts which allow them to use it the most, and they may become good at things which require it. This is basically what Gifts Differing & MBTI sought to do - make correlations between type & strengths to guide people in choosing careers based on what social roles they require. It's misleading when people take it to mean that X type is good at Y. Many different types can be good or drawn to the same thing because there's not one way to approach most things. However, sometimes social roles dictate that you have to have a certain mindset (or personality) to make that thing your job, and MBTI was sort of bridging that gap to help individuals find their niche in society, not to box them in or limit them.
An example of this might be the idea that INFPs don't make good leaders. I'd disagree - we may not make good leaders according to the cultural idea of what is "good" or what it means to lead. Most culture/society/whatever say INFPs are better suited to occupations in the arts, spirituality, etc, and in pursuing these, they are more likely to find their mindset accepted & rewarded. It's a matter of their social niche, not their strengths or abilities or even desires. The problem is not everyone finds their personality & social role matching up, which is not problem outside of typing people. It's only when typing people that social role can be blinding to what mindset a person has, and that's when you have the Keirsian philosophy of typing all artists as ISFP (or whatever).
I'm on a tangent now....but I think I made a few points .