The main advantage of a five link on a live axle is for handling increased engine power output.
Live axles that have only the leaf spring for location are ok on a relatively light car with low power outputs such as the early 4/4 Series cars and 1300cc Ford Escort Mark 1s and 2s. Increased power output, competition and race starts stress the springs incredibly; they contort themselves into an 'S' shape, cause axle tramp and generally wreck axles. That's why rally spec RWD Escorts run five link axles and why a race Morgan generally will have anti-tramp bars unless restricted by in-period spec regulations.
Coils are a big improvement and do away with a long, flexible, heavy and generally uneasily changeable spring-rated means of providing both suspension and axle location.
But they together with the obsolete and idiosyncratic front suspension they are part of the car's character and charm. For some inexplicable reason, they work after a fashion and make their archaic contribution together with the coach-built bodywork to the essence of a Morgan!
