It is all about actual air flow, not just how the ducting is mechanically configured.

In a previous house I owned some of the floor registers were at the ends of very long 5 inch air ducts. The ducting was mostly straight runs, but overall was so long that the aggregate air flow reduction meant I could lay a facial tissue on each floor grill and it would not blow away.

Upgraded that room to a 10 inch round duct, plus better return air capacity (added another large duct). End result was the air flow was multiple times more effective. The AC could now easily keep up with the south facing large windows.

Ducting matters. Return air in houses is often given short shrift if it considered at all. 100% of the air that flows out into your rooms must also flow back to the furnace/AC fan. Get the return air flow right sized and properly located, and the rest of the HVAC system can do its job properly.