I’ve been shooting a 20 ga for 20+ years. I shoot one because I like the way they feel and handle not because i think they are the best tool.
For big ducks they are best suited for decoying birds at short to moderate range 35 yards and in using 2-4 shot steel w/appropriate choke.
For longer range shooting 40+ yards with steel I like bigger shot than #2 and don’t think a 20 ga throws enough of the bigger shot for a very effective pattern.
With that said if one wants to pony up some more money and shoot some of the heavier than steel shells the 20ga becomes a more lethal tool at longer ranges. Like woodmaster81 says the tungsten matrix is great. Shoots like lead and
#5’s work like a champ but I can’t bring myself to pay the high price for them. Bismuth is getting more affordable and worth trying.