Test specialists eventually stagnate to be honest. We don't play enough Tests and those who only play that format don't really develop their game. Always better to have dynamic and versatile players who can play multiple formats, ideally all three.
We need to identify a core of 5-6 players who play across all formats. Most of the successful teams have such a core, e.g. Australia - Smith, Warner, Starc, Hazlewood, Khawaja, India - Kohli, Ashwin, Rahul, Shami, Jadeja, England - Root, Stokes, Bairstow, Buttler, South Africa - QdK, Rabada, du Plessis, Amla, de Villiers (although the latter two not for long). At the moment, we are lacking such players. Apart from Sarfraz, Babar and Amir (who has been woeful in Tests since his comeback), we lack such players.
