You ask a great question and there is a lot of debate going behind the scenes.
A focal plane with 25um pixels will have 4 times the area of a 12um so you would think 4 times the performance but yet the new 12um systems seem to be the best image, this does not make sense.
The best way to explain without going into Too much detail is that newer technology, process, fabrication and materials yields better sensitivity and combined with newer techniques with coding and algorithms yields better post processing.
The goal is in our space SWAP, size weight and power so smaller is better. If you made a 38um focal plane today it would completely outperform the 12um but we are not and what you compare sometimes is 10 year difference in technology.
So for now smaller is better, cannot believe I said that.