It is a fact that in recent years there could have been further improvement in their diesel technology. Especially wrt emissions and smaller displacement and better power and torque characteristics. To develop something extraordinary is not something that Toyota lacks; its just it enjoys unquestionable trust when it comes to overall experience and therefore customers really don't soo much look in minute details about Toyota technology here. A good case study is Lexus LFA development if you can see their laboratory which is now rarely used to push limits of engine capabilities. So yes they do get away with yesteryear technologies for too long before bringing a major product range and product life-cycle management. Also MJD is a product of GM and Fiat collaboration and therefore is a result of massive efforts to product clean(er) diesel technology along with reasonable performance benefits. VWs major fiascos aside, it will still be unwise to underestimate their group capabilities to produce reliable next gen super efficient diesel tech.