You can directly download your games from GOG inside Lutris, no additional software needed. Same thing for Heroic Games Launcher.

Having an open protocol to get your games is way more important than a dedicated client, because it goes against the kind of artificial market fragmentation we see in the Streaming world with every service having their own dedicated client (times the number of platforms they support) instead of people being able to just have one client for everything.

IMHO the experience with GOG games in Lutris is superior to that with Steam games and the Steam client because Lutris doesn’t get in your way when all you want is to play the damned game, whilst Steam always fires up the full client and at times even starts updating before you can even start the game and even defaults to starting the client on their shop-front and the user has to figure out where in the configuration they can change that if they want otherwise.

I can see your point, but it’s a pretty weak reason if at all valid, IMHO.