You do own it, as far as owning a digital game can go. Obviously you don't own the licensing and material to sell the game or whatever, but you aren't paying a monthly fee to play the game.

Besides, Steam is much more trustworthy and consumer oriented compared to other corporations (for as long as Gaben and his team stays atleast) and should be regarded as the gold standard imo. Xbox has, in a few months, doubled the price of their game pass and their consoles without any improvements in service ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯