I think steam has a pretty consistent 30% steam-tax on all games, no preferential treatment. If some titles were getting a better deal from steam than others, that wouldn't be a great ecosystem for devs.
Happy to be proved wrong though.
I guess you missed this news last year.
https://www.kitguru.net/gaming/matthew-wilson/valve-announces-changes-to-steams-revenue-cut/The Steam Distribution Agreement was changed last Friday in an effort to give development studios a larger share. Unfortunately, this bigger cut only applies if you can sell a large number of games to begin with. Going forward, Valve will still take its standard 30% cut from games that make less than $10 million. Games that generate between $10 million and $50 million in revenue will only see 25% of that revenue taken by Valve. Meanwhile, games that generate more than $50 million will see an increased saving, with the Valve tax reduced to 20%. This change will affect all revenue earned from the 1st of October 2018 onwards.