Handwaver

Take his predictions about our technological and business-development timelines with a grain of salt, because he's an inveterate handwaver.

Source: wiktionary

It is easy to lose sight of the fact that the oversimplified model that is eddy diffusion must be used with care and with a great deal of auxiliary physical insight. Well-educated handwavers often produce more useful results than the people who concentrate on the mathematical and computational aspects of the problem. The ideal is a suitable combination of the two. One way to become well-educated is to study various limiting cases that can be solved analytically. Indeed, these solutions can take us surprisingly far into many problems, sometimes rivalling what can be done with a computer. The substance of this article is a summary of the available solutions, and a critical compilation of eddy coefficients for the atmospheres of the Earth and a few other objects.

Source: wiktionary

It is quite inconceivable that any handwaver could ever have dreamt up the use of a pendulum to measure dissolved carbon concentrations!

Source: wiktionary

A gifted pupil might sometimes need to be coached privately about avoiding presenting themself as a handwaver.

Source: wiktionary