In defence of the full sinking line.
Full sinkers are easier to speycast than sunktips, you just roll them to the surface then start the cast. With sinktips there is little control of the lift.
To control the speed you simply alter tha angle of the cast, to fish the fly slowly throw a long line with a narrow angle the quickly before the line settles thrrow in a big memd feeding more line in if you wish. Sunk lines fisher slower than sunk tips as the deeper you sink the slowert the current.
A sunk line gets down quickly compared with sunk tips