H,
Over the years I have had 2 rods break , both at the tip section through pulling line down through the rings, I know now that this is a BAD thing.

The joint on a rod is , I would have thought , the strongest part especially when the rod is assembled as there are two thicknesses of material, albeit slightly thinner walled than the rest of the rod.
The argument against multi-piece rods was that early ones were lumpy when casting as the joints flexed less than the rest of the rod.Modern ones do not suffer from this , or at least I cannot tell by casting alone if a rod is 2 or 4 piece
I have a 2 and 4 piece Sage rod of the same model . I liked the 2 piece so much I wanted to use it on my travels and bought the 4.I would defy anyone to blind test the difference.
Now, all the new rods I buy are 4 piece
Regards
Rob