Four Link Suspension, how does it work?

The simple, but very incomplete answer is a four link allows a change in the leverage, and angle it is applied. A ladder bar has a set leverage length of about 30 inch to 36 inch, from the axle center to the front bolt.
The ladderbar angle change is fairly limited, usually higher or lower no more than a spread of 4 inch.
A four link has many more choices .
Each power level at launch will like a certain amount of down force on the rear axle. The higher the launch power, the less leverage you MAY need.With a ladderbar setup, the rear shocks need to moderate the leverage. The down side of that is if you need a lot of launch control with shocks and a ladderbar, it can affect downtrack performance, since the shocks may need to be set real stiff on extension.
I run a ladderbar on a 980 hp 2900 lb dart. My shocks need to be set tight, and i leave at only 3800 rpm/part throttle to get good consistant 60 fts. At this level of power and starting line ratio of 11/1, a fourlink should work better, but it is qhat i built many years ago.