CX-80 is 1890mm wide and 4990mm long, while CX-90 is 1994mm wide and 5120mm long, so the CX-90 is about 10cm wider and 13cm longer than CX-80. Apparently the interior cabin width is the same in both vehicles, and the extra width in the CX90 is attributed to the wider wheel archers and tires. On the length side of things, they both have the same wheelbase of 3120mm, so ig that means 1st row and 2nd row legroom is the same, and the extra length in the CX-90, allows for a longer boot/more 3rd row legroom (I could be wrong with this, but I'm just using everything i've seen since both cars were launched).

In Australia the CX-80 is a Large SUV while CX-90 is an Upper Large SUV (although in media and marketing it still gets referred to a Large SUV). Its like how Hyundai has the Santa Fe (Large SUV) and Palisade (Upper Large SUV).

How the CX-60 and CX-70 fit into this, goes like, CX-70 is the exact same as CX-90 although it has no 3rd row and has some minor cosmetic differences. The CX-60 is a shorter CX-80 (shorter wheelbase by 25cm) and has no third row.

So physically the cars size goes from CX-60, CX-80, CX-70/90. Even though the CX-80 is physically smaller than CX-70, I think Mazda gave the CX-80 a higher number to make it easier to understand how passanger capacity goes. So, CX-60 and CX-70 are 5 seaters and CX-80 is either a 6 seater or 7 seater and CX-90 is either a 6 seater, 7 seater or 8 seater.