Do you really think that Amazon and Walmart don’t meaningfully compete? What about Ford and GM? Android and iOS?
There are on the order of 10 video game companies with over a billion usd in revenue. There are 3 distinct console manufacturers (4 if you count the steam deck, 5 if you include PCs). Then there’s the mobile gaming market, which has all the big players plus a bunch of others.
Duopoly’s and small markets goodness or badness is irrelevant in this situation.