Apparently most of Japans rail/transit operators are private not public; with the largest company making $10 billion in revenue. Hong Kongs MTR is also for-profit and has a head start expanding into mainland China and to four international markets.
The two companies were about the same size in terms of revenue in 2010, but MTR's top line grew 83% to reach $6.8 billion in the eight years since, making it 1.7 times larger than Tokyo Metro. During the same period, Tokyo Metro's revenue has increased by only 17%.
Graph of the worlds busiest Metro systems is here https://www.ft.com/__origami/service/image/v2/images/raw/https%3A%2F%2Fs3-ap-northeast-1.amazonaws.com%2Fpsh-ex-ftnikkei-3937bb4%2Fimages%2F_aliases%2Farticleimage%2F3%2F2%2F4%2F4%2F23264423-1-eng-GB%2F20191030-World-Metro-BubbleBar.png
Tokyo has 3.46 billion annual passengers(?) and 400 km of track. NY has 1.81 billion annual passengers and about the same track. The longest track is Shanghai with 600 km of track and 2 billion passengers.