This is not true since Valve/Steam is seeing growth from solely being the default/defacto place to play in gaming & this is partly from all PC games releasing on Steam giving Valve/Steam by default exclusive games that aren’t on Epic or consoles.
Lethal Company, Rust, DayZ, PUBG, AmongUs, Counter Strike, Deadlock etc are all Steam exclusive & where exclusive for 3-5 years if not longer & in some cases permanently. The only publisher to really compete w Valve/Steam in PC are Riot since there games are exclusively & permanently exclusive on the Riot launcher & they continue to see growth & profits. It’s not a secret that growth & profits comes from actually producing games & in the cases of storefronts having permanent exclusive that bends the knees of other competitors till they submit ie ABK games on Steam, EA games on Steam etc etc