Back in the dark ages Turbo's were free floating ie: No WG at all and were sized to work in a very narrow powerband, not so great for cars where the widest possible powerband is desirable.
If you installed a tighter turbine housing it improved low and mid range response but would overspeed the turbo causing failure, enter the WG, it's job is to control the turbine speed anything else is secondary.
Internal gates are a poor second to a quality external as by design the tend to "creep" and do blow the valve off the seat causing lag when used with a low spring pressure actuator.
An external will plumb some boost into the back of the diaphram via an EBC to assist the light spring and this combination allows as low as 3 psi to be set and maintained as well as whatever high setting is desired without the creep caused by the small flapper internal valve
If you make the flapper bigger to prevent creep the increased area requires a stiffer spring to hold it on the seat, there are some rare dual valve internal gate turbine housings around.
