I am replacing an existing furnace/AC with a new HP/furnace of pretty similar size. I have been wondering about the significant difference in flow to various registers. The current duct work basically has a major duct that goes left from the furnace and another that goes right - both in finished soffits. Each of these major ducts feeds one side of the house or the other in this 2 story house there are mini-trusses between the floors.

Initially this didn't make much sense to me. However, on closer examination I notice the the duct with greater apparent flow appears to come directly out of the furnace/coil and feeds the right side of the house. The other duct comes out at 90 degrees to the first and within a couple feet makes a 90 degree turn to pretty much go 180 degrees in the opposite direction of the first spur as I would expect.

Is it probable that this 90 degree turn has caused a major imbalance in the air flow to the weaker, left side of the house? I would appreciate it if somebody could help me to understand if it is possible with out a great deal of add-on work and damage to finished areas to at least balance the flow in each major duct.