I think sink tips are much harder to learn to cast. They are basically a short area of sink. Like putting a bunch of split shot on. A chuck and duck.
Full sink lines are smaller diameter and much easier to cast than even a floating line. Plus, keeps the fly in the zone when stripping it in.
I use a DENSITY COMPENSATED Type II on rivers when fishing streamers AND softhackles (perfect presentation for these) And a Type III in a WET CELL
when fishing weedy rivers or stillwaters.
Plus to me, the smaller diameter is much easier to lift. No mending, just cast across and drift, or down and strip.