No I don't own a G9. Have you tried a Sony A7cII?
I've had MFT since the GF1, I've had multiple Panasonic bodies and lenses and here's my opinion.
MFT will not give you the ultimate file image quality of a "FF" system of anything like a similar tech generation even in good light if you go looking for the differences, it's just not going to happen. You can just not look for the differences and be happy or you can give MFT the best possible chance by using good lenses at wider apertures.
For me MFT makes less sense these days when FF cameras like the A7c range and even the A7 series mini SLR bodies exist as they can be smaller than a MFT camera like the G9 plus there are compact FF primes too. Here's your G9 and two cameras I have, Sony A7III and A7cII...
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That's why I've sold most of my MFT kit and now just have one RF style camera and four lenses two of which are zooms, the 45-150mm and the 100-400mm. One problem with the 100-400mm is the aperture range which when coupled to a smaller sensor is not going to do you too many favours. MFT and longer lenses are very probably going to be smaller, lighter and probably cheaper than the FF alternatives though, so there's that but lets not kid ourselves that MFT is going to equal let alone get you better IQ than FF if you go looking for the differences. It simply isn't.
I feel the same about APS-C these days too. I think the supposed advantage of size and weight can melt away unless with specific combinations particularly with longer lenses and IQ wise these smaller systems are going to take at least some IQ hit... if you go looking and care about the differences. Not that FF is the ultimate though as there are larger systems but bang for £ wise FF is enough for me.
I don't really like commenting on the quality of other peoples pictures as when posting here pictures can often look soft and that might be the case with your picture as on my screen nothing looks sharp and I can't tell where you've focussed. I wouldn't be looking at that picture as an advert for MFT. Sorry.
If just starting out now and looking at a budget of £600 I'd look at the earlier A7 cameras. I had the original A7 for 7 years or more. One of those or an A7II with a Sony 35mm f2.8 or 28mm f2 will probably be well within budget or there's the original 28-70mm f3.5-5.6 or the newer collapsible 28-60mm f4-5.6. I've had both. Might even get two lenses within budget, a prime and a zoom, which might be more use as a general and holiday combination / set up than a MFT camera with 100-400mm lens. YMMV.
I used to take my Sony A7 and 35mm f2.8 on holidays but these days I take my A7cII and 40mm f2.5.
Sorry for the long reply. Just trying to be clear and give the OP my honest opinion. Hope it helps.