Also the different engine are created for different needs.
Some user very seldom use a render engine and need basic render output only, this people could use the Rhino renderer or nXt.
Other people have no problem with longer render times, but like to get an easy to use engine and photoreal render output.
This engine doesn’t allow the user to grow over the years, the render speed will not be better by the knowledge of the user. There are no tricks. This engines are good for medium res and not so good for interiors
Other engine allow to choose between a handful of parameters to get more speed, but some knowledge is needed to keep the quality. Over the years the user will be better and better and for example he can easy render extreme large images based on short render times.
Some engine are universal to use - photoreal, graphic use, user shader tools, … and the prices are different. Some engine are using the graphic card only, other one allow to use several machines for rendering over LAN. Some are good for product shots, some are better for jewelry, … .