Jadeja is an ATG because you are getting a complete package.
1) A Stuart Broad level bowler. Jaddu averages 24 with bowl but I do agree it is slightly inflated due to spin pitches in India. In a more balanced world, hai average would have been 27-28. So, rightly a Stuart Broad level bowler.
2) An Imran Khan level batsman. Imran played on flat pitches and averaged 37. His batting stats are highly padded by runs on home pitches and final 15 tests where he played as specialist batsman. Jadeja is a bit unlucky here as he got turners at home and seamer friendly wickets away. Inspite of all this, he averages a very solid 34 with the bat.
3) Not only this but Jadeja is also a spectacular fielder, in the league of Smith and Stokes as fielders and is arguably the greatest fielder to come from Asia.
All in all, a true Test ATG of this generation and best since Kallis.