It's 1/2 inch for the old sensor vs 1/1.28 for the new. So the newer is about twice as big.

"plans to install a LARGER 1/1.28-inch camera sensor with up to 133% better light performance than the 1/1.2-inch.."  You understand that's a fraction, right? So the bigger the denominator, the smaller the sensor. So what you've stated doesn't make sense.  Either the new sensor is than the old, or you've gotten your numbers mixed up.  So which is it?

The 1/1.25" sensors definitely will improve light sensitivity... but we still don't know what the real resolution of the sensors are. They never revealed the X4's real resolution either and all indications are that it uses the exact same 5.7K sensor as the X3 then AI upscaling to 8K.

The newer, larger sensor could genuinely be an 8K (or more likely, 11.4K) sensor, but we may never know.

If you're using the X4 or X5 to reframe to 4K video, then this is probably fine since you have 5.7K upscaled to 8K to work with, but if you want to do VR grade 360 photos, then you want higher real rez.