Do you want to compare with FF or APS-C. I know another poster already accused you of moving the goal posts and I am right now experiencing the same thing. No point in pursuing the argument.
All I can say is that the differences in IQ are minute when you also take size and weight into account. People should think more for themselves instead of blindly trusting reviewers who are largely interested in selling stuff (because new gear is their content).
In the end, there is no free lunch. If you want significantly better IQ your equipment will be significantly larger and more expensive.
In both cases the similitude applies you don't compare a prime at the same aperture you need to apply equivalence the other way around hence at least f/4 when you look at 300mm vs the 200mm of a MFT the relative crop is 1.33 so a 32 Megapixel full frame will have the same weight and have more DR etc etc etc.
The same 300 f.4 on APSC will be 450mm so no need to crop and still lighter with more magnification.
Ultimately the promise of MFT as per the own Olympus mission statement was a radical reduction of size, weight and thickness but this no longer works once you have a 1.2 Kg lens really or 750 grams for a mid range zoom the reduction of weight and size is minimal to none and the IQ is not better so people don't need to stick around the format anymore. Now they may leave to a mobile phone regardless but that's another story
A common misconception is that larger sensor capture more light but actually larger physical aperture capture more light and therefore larger sensor capture also more light as they have larger lenses. Size does matter when you are chasing light so you can promise weight reduction only if you get less of it!
Fortunately for us underwater photography and video is a small aperture game and within this game equivalence does matter and therefore APSC=Full Frame=MFT due to equivalence we don't shoot tele lens or fast lenses. At the end what matters more are ergonomics, AF etc etc not sensor size despite lots of people here think differently. But this does not hold true for the general public so we need to hope there will still be MFT cameras for underwater use as it is a great format and if you don't go on my path it can be compact too
