On a well designed rod, you will not notice any difference between a 2 piece model or 4 piece model. Whether that difference is weight or action. The functionality is the same.
If ferrules are loosening, which does happen every now and then on even the most expensive multi-piece rods (even 2 piece), add some wax or grafitoline (
http://www.flugor.se/bild_arkiv/big_2622.jpg )
Spey fishermen using double handed rods actually tape the ferrules on their rods so they do not loosen. Why? Because during the cast, the blank actually twists and the ferrules loosen on their own. It's not the rods fault, only simple "physics" of the cast, if you want to call it that.
The same thing happens with single hand 2 piece, 4 piece, 6 piece....rods. Your casting stroke causes the ferrules to loosen. Again, we're talking about good quality rods, not 4 piece shakespeare rods from Wal Mart.
If you are a caster that brings your backcast to the side, then over the top for the forward cast, you are more prone for ferrules loosening than others. During the transition from the horizontal to verticle position of the rod, the blank twists due to the weight of the line and the directional movement of the rod. Do this at home or on the stream and watch the rod itself. You will be surprised.
The weight? The weight is not a factor. Look at any of the new 4pc-6pc model rods. The Orvis Helio's is a great example. The 9' 10wt saltwater model is 3.5 oz...... Rod design is critical.
Action? What do you like? Slow, Moderate, Fast? You can find any action you like in a multipiece rod. Being broomsticks is a false stereotype.
Sales dictate the manufacturing and development of new products. Manufacturers sell more 4pc rod models than 2pc, and 3pc are becoming more endangered every day. This is what most people want, not what the big boys are forcing on us.
Best,
Fisher