When I swapped over to micro 4/3 I thought the sensor was half size... ?
A couple of years later, I finally found out it was actually only 1/4 the size.... of what I really wanted.
Funny thing is that the entire camera industry is being slowly killed by smartphones which have only 40mm² sensors (iPhone) with an active area thats only
1/25th of what you really wanted.
Let's be honest. How often does even ILC owner bother to pick up the
good camera instead of just taking the photo or video with the smartphone that is
good enough camera. That's why smartphones are eating even ILC market share: also ILC owners are using smartphones for casual shooting because they are fine with 40mm² sensor quality under good conditions.
Discussion about ILC sensor size is almost irrelevant because technology has already reached the point where it can match the human vision in all but exteme conditions with MFTs 225mm² sensor and exceed what is considered to be "good enough" for 98% of humanity with 40mm²
Even FF bandwagon doesn't try to claim that average human eye (professionals call them "paying customers") can see any sensor size based difference between FF and MTF images or video under good or even typical conditions. It's all about this low light performance whatever that is and I am indeed constantly checking if I would get more bang for the buck if I switch from MFT to mirrorless FF.
I don't even consider crop frame sensors because they are just as bad as MTF compared to FF under very low light and yet they cost the same or even more than FF. It's obvious that crop frame is dead now that budget FF cameras with good specs have emerged from the very same manufacturers who used to have crop frame as a budget option.
Test sites like DPR where you can compare studio scene RAW images between 4 cameras and different ISO settings are an excellent tool that anyone considering new camera should check. So here are the latest conclusions I have made when I compare M1.3 and Pana G9 with 30-100% more expensive "budget" FF bodies (compared to local G9 sale).
There seems to be a consensus that 3200 is the max ISO where MTF images or video are still usable and I agree with that. If I compare MTF RAW 3200 images against FF at higher ISO the subjective quality (noise, resolution, colour, dynamic) will become equal at 12 800 for Nikon Z6 and Pana S1 which seems to have pretty much best low light noise profile of any FF camera. This is in line with the real world experience I get when I compare my MTF F1.4 prime photos and video shot in indoor sports arena with ones my friend shot with FF and F2.8 prime (they always have annoyingly dim lights for sports shooting).
It looks like 1300€ and 5300€ FF cameras use same sensor technology as well and price difference comes from elsewhere. Greatest surprise was that Canon R/RP absolutely sucks after ISO 3200. Yes, it's still better than MFT but nearly on par with best crop frame sensors like X-T4 and visibly below Z6 and S1. It's also strange that Canon R JPG must be the worst in the industry, whereas Panasonic excels here. JPG from Pana MFT at ISO 3200 looks practically as good as Canon R/RP at the same ISO.
Conclusion: since I own a couple of excellent and really inexpensive F1.4-1.7 MFT prime lenses which cover the focal range I might need under low light, I have never found any reason to shoot above ISO 3200. That being said: I would of course be happy to shoot those at ISO 800 or with faster shutter speeds but the cost of this improvement would make no sense to me. Photography is a (serious) hobby for me but not the only one and I can easily find several other ways to spend 2000-3000€