Steam is undoubtedly inconvenient. Imagine a third party proprietary launcher filled with ads was required to use your browser.
The only “ad” steam pushes into your face is the startup pop-up, which can be disabled in settings.
Without that, you can use whatever you like to launch your games. Valve doesn’t care. You can have a desktop shortcut for every one of your games and never see steam open, or use something like PlayNite to aggregate the games from several services into one library.
You can use steam without ever seeing an ad. Due to low internet bandwidth I just turned off the couple of popups and I currently see 0 ads if I don’t specifically go to the store part. Steam boots into library, so no ads, none in downloads. I don’t use the rest unless I’m actually looking for a new game.