One side of the house has very poor heat pressure

Red Squirrel

I have a split level house and the lower side seems to have very poor air pressure when the furnace is on. I can barely feel the air coming out of any of the vents. The dampers are all open as far as I can tell (handle is parallel with pipe) but they are very loose so I'm wondering if the damper got loose and is in fact off, any way to tell?

There is a total of 7 vents and one return. The 7 vents are connected to the same rectangular duct leading to the furnace. It all looks normal and standard.

The other half of the house has a total of 6 vents and 1 return connecting to another rectangular vent that then goes to the furnace.

There's also a vent downstairs that is actually connected to the return duct. So it seems to me my vent/return ratio is ok, but any proper way to tell, do I measure the square inch of all combined vents and compare it with the returns?

Also since heat rises, could it be it's just being forced to the upper pipes instead of going down to the crawlspace vent?

There's also a bit of air loss along the vents but that can't be enough for such a drastic drop, or can it? I could try to patch all the pipe joints with aluminum tape.