Rocket Engine with 0 - 100% Throttle Range

I wondered why the rockets couldn't accelerate slowly until they reach higher altitudes to minimize air drag and surface overheat. Here are the specs of the two famous rocket engines:

SpaceX Merlin Engine (Falcon9) throttle range is 40 - 100%

SpaceX Raptor Engine (Starship) throttle range is 40 - 100%

With such throttle ranges you cannot accelerate slowly. Here is a NASA paper explaining the reasons limiting throttle ability. A Historical Systems Study of Liquid Rocket Engine Throttling Capabilities

The sliding rocket engine I had proposed earlier can be throttled to almost zero level because it lacks a turbopump and propellent cooling. In combination with the Piezoelectric injectors, the rocket can be accelerated extremely slowly. Here is an article on the new type of injectors Simulation of Piezoelectric Injectors on Rocket Engines. 

The advantages of slow acceleration: Less energy loss due to air drag, less heat on the rocket casing, much less air drag allows larger diameter payload deployable.