I was into Fuji quite deep with X-T20, X-H1 and later X-S10 and was seriously considering the X-H2s as replacement of all above. I never gave huge attention about M43 until some friend (he earns money using canon) told about how great this system is. Renting a E-M1 III with two lenses for a weekend were opening my eyes. The 300mm F4 was simply stunning and I realized how bad actually my 2 copies of the XF100-400 were and how many times i came back home with not even one usable photo because of ibis issues, softness, lack of AF, etc. With Fuji I was then using adapters and a 150-600 FF Tele but its been a monster with moderate AF and IQ. I have also rented the old version of the 12-40 F2,8 and its been great as well. Comparing photos from this weekend lastly made me to sell my complete Fuji set including approx. 15 lenses and invested blindy (pre order) into 2x OM-1, one as the kit variant with the new 12-40mm f2,8 which I can highly recommend. Since there photography makes more fun again to me. It is the ease of the software actually which makes this happen. Everything works splendid, the mobile app, life ND, Highres, life composite, etc. I first thought these modes are empty marketing highlights but no, they work very well - every time. The biggest improvement for me coming from Fuji is the way better software and AF, the ease of switching shooting styles on the fly meaning long exposure, life ND, Astro, life composite, macro (the 60mm is cheap, light and fits in every jacket) and all combined with the incredible Ibis. No need for a tripod.
The only regret is why I did not consider M43 earlier, especially when I remember about how many times I came back with zero usable photo with Fuji when i went out for wildlife.
To be fair, Fuji deliveres in street, people, landscape, but for me had huge lacks in the other parts. The Oly does the above well and the other exceptional good. The IQ differences are minimal and the ISO capaility of the OM-1 is better than with the Fuji models I had.
Anyway, I suggest you to rent the gear you consider and get your impressions first hand.
Attention: since I have not touched a Fuji for more then a year I cannot say how things were improved in their latest equipment.