My observation is Nikon screwed the pooch and clung to a system 30 years beyond it's shelf life. Canon innovated and were bashed for it until it was seen by pros as the future and taht's all she wrote. Nikon is still struggling. Yes the D850 is good but it was still the old F mount with all the limitations.
Actually, part of Nikon's problem was the other way around: they spent too much money developing mirrorless trying to keep pace with Sony.
Sony paid for its R&D by profits from semi-conductors, as was their plan considering they are the global giants in the sector, THEN re-align divisions so that each had to stand independently. (That ultimately semi-failed and they had to buy back their own division, deviating from their purely parent holding company strategy.)
Mitarai, the CEO of Canon, just loved this because he takes a very solid, predictable, and dependable approach to product development (and the company as a whole) and was well aware that Nikon would be forced to restructure. This was going to, and did, lead to Nikon having to make some major changes, including cuts to even how many cameras they could produce and move, i.e. supply chain optimization particularly of its imaging products business.
Ending fiscal year March 31, 2019, revenue decreased 1.2% yet operating profits increased 47%.
Their cameras didn't get 47% better, they didn't sell 47% more cameras, reviewers on YouTube didn't give Nikon 47% more positive reviews.
This change had absolutely nothing to do with products and/or features of products. This had nothing to do with things like the F mount.
What happens is that photographers go to websites, watch videos, try gear at stores/as rentals, then just start making up claims regarding a corporation's profitability and management based on whether or not product X has nice buttons or by liking or not liking the framerate 4k video is shot in.
It's not reality though, far from it.
Nikon's big problems? Bloated and inefficient logistics, lack of capital investments in overseas biomedical, not enough focus on FPD lithography, particularly large panels (which they turned into a 53.1% increase in operating profit last year!! sheesh).