Route return air duct through attic or pantry

I’m looking to get feedback about my options to remediate uneven heating/cooling and poor airflow for two of our bedrooms. Any help or ideas are much appreciated. I'll do my best to provide as much information as I can and answer any questions. Suggestions are welcome!

General info

My house is a 2 story colonial house built in 2011 in Southeast Michigan. The house is rectangular with the 2 car garage occupying a corner, so the living space is roughly L shaped. The basement is insulated but otherwise unfinished and the attic is unconditioned. The utilities (air handler, furnace, water heater, etc.) are all located on one end of the basement (in the small part of the L). The HVAC and other equipment are original to the house and in good condition. There are no interior walls that are stacked.

Here is a sketch of the general layout from the township website^†:

† Note: the layout is not completely accurate (but good enough). The areas marked SLB (slab?) are not on slab and have basement underneath. TWD is our treated wood deck and CCP is the porch.

Problem

The upstairs gets very hot in the summer and takes a long time to cool, particularly in two of the bedrooms, including the primary bedroom, which are the furthest from the air handler. While the blower is running the return air registers in these rooms measures 0 CFM. Thus, air is not flowing through the return air ducts out of these rooms.

Through some investigation, I found what the return air duct path should be. The return air from each room should travel pull down through the wall to under the 2nd floor. Then it would travel down an interior wall on the 1st floor to the basement. In the basement it would connect to the main return air trunk.

However the 1st floor interior wall was removed by a previous owner, as you can see from this photo:

I've spoken with a contractor who came up with 2 options:

Option 1

Reroute the return air through the unconditioned attic. This would involve installing a boot, running insulated flex duct across the length of the house (45') into the garage attic, punching a hole in the garage ceiling, continuing the duct down the side of the garage wall, and then popping into the basement through the rim joist.

We'd lose some garage storage space and I'd probably end up putting drywall around the flex duct in the garage. This option would allow both bedrooms to be reconnected to the return air trunk.

I'm decently confident I could do a lot of this myself. Joining flex duct together doesn't seem too hard but installing the boot and connecting to the return trunk is more daunting.

Option 2

Use part of the original return air path to get the air from the 2nd floor to 1st floor, but bring it into the nearby pantry to connect to the basement. This would involve widening the soffit around an existing beam and punching some holes into the pantry. We'd lose about a 1/4 of the storage space, maybe a little more.

While this seems pretty straight forward to me, I have no experience with drywall or building soffits.

What is my best option?

Which option would best fix my problem? I'd really hate to put in work or spend money and not fix the problem; I also don't want to do anything more or spend any more than I have to.