One thing to remember for all engines in general is that they can not be designed to operate their best at all RPM ranges. So they are designed by the engineers to produce the best torque, HP and efficiency in a specific RPM range for the application (which is definitely not at low RPM for a large engine)
That being said, even with a large 4 cycle engine, forcing it to troll all-day is not really what it was designed for. Granted that the 4 cycle engine is more tolerant to low speed operation than the 2 cycle engine, but it is till not designed to operate at low RPM's for an extended period of time.
The kicker engines are designed with a much different power curve which allows them to produce torque, HP, and efficiency at a much lower RPM than a large engine. They do this in 4 cycle engines through camshaft timing design variations (and sometimes compression) and in 2 cycle engines the port design and exhaust system are designed optimize low RPM torque, HP, and efficiency.
(no opinions here just information)
I personally use a 4 cycle kicker for trolling