Thresh is not tank!
After the reveal of the updated classification system I feel much more confident in saying this. He is somewhat durable (more than bruisers but less than juggernauts/wardens/vanguards) so don't expect him to front line for your team by himself unless your team is ahead enough. He is good at making picks, not starting team fights unless he gets the magic hook on squishy/carry past the front line or by flanking. If your picking Thresh because you want/need a warden or vanguard on your team and not his pick potential then I suggest picking another champion before you become disappointed.
RITO FINALLY GAVE HIM A CLASSIFICATION THAT FITS HIM. THANK YOU
. I really hope they look into items that tailor to this class specifically that wont be abused by other classes in general. This
is like the poster boy for catchers currently IMO.