Horsepucky. The top end is the EM-1 II or III for most and even if matched with the 300 - for birding - is way lighter and better than any quality Canon or Nikon set.
E-M1 II + 300mm f/4 PRO -> $3,950, 2050g
D7500 + 300mm f/4 PF VR + TC-1.4E III -> $3,400, 1650g
The Nikon combo has same max aperture (75mm), 5% more reach (630mm FFE to 600mm FFE) both on 20MP, and better tracking AF for following those birds.
Tell me why I'd want to spend 16% more money to carry 24% more weight and get worse AF performance.
Maybe because the 300mm f/4 pro is significantly sharper even against the bare 300mm f/4 PF, much less with TC-1.4E attached, especially when you stray from the center of the image?
Thank you. I deliberately chose the 300mm PF and TC combo knowing it was likely a little less sharp than the 300mm f/4 PRO, because I wanted to see If I could get an MFT fan to admit it was OK to buy heavier and more expensive gear to get better IQ. We usually hear the opposite.
Having accomplished that, let's now consider substituting the AF-S 500mm f/5.6E PF ED VR for the 300mm PF and TC combo. As you can see, ephotozine rates the 500m PF as sharper than the 300mm F/4 PRO.
https://www.ephotozine.com/article/nikon-af-s-nikkor-500mm-f-5-6e-pf-ed-vr-review-33044
The substitution adds $1,100 to the price and 515g to the weight, and provides 25% more reach then the Oly. The price and weight adjustment makes the Nikon combo 14% more expensive and 5% heavier than the Oly combo. If it was worth spending 16% more and carrying 24% more weight to get the extra sharpness of the Oly, wouldn't it be worth spending 14% more and carrying 5% more weight to get the extra sharpness and reach provided by the 500mm PF combo?
The chart on the right certainly doesn't seem to agree with the chart on the left. On the whole I'm leery about comparing performance of a lens tested by one site against performance of a different lens tested by a different site. The significant differences between the left chart and right chart for the 300PF should tell you why. Above I compared the performance of the 500mm PF against the 300mm f/4 PRO as tested at
the same site.
Photography Life don't seem to have gotten around to measuring the performance of the 300mm PRO. If they did, I think we should expect it to be less than the ephotozine results by about as much as the 300mm PF on PL is lower than the ephotozine results, due to systematic differences as to how they test.
Goes to show just looking at aperture equivalence doesn't tell you the whole story.
From what I can tell also, the TC in the Nikon also lowers your keeper rate.
https://www.dpreview.com/forums/thread/4127480
He was using the older TC II on an old lens. AF performance with the 300PF and TC 1.4E III is much improved. I expect keeper rate with the 300 PF and TC-1.4E III will be better than with the Oly combo due to the Nikon's far superior tracking.