No, it doesn't weak anything. The PlayStation brand is more successful now than it has never been looking at their revenue, console sales, game sales or even exclusive sales. People buy PlayStations because they know it will have a ton of great games they want to play.With them coming to other platforms it weakens the need and the branding for playstation though. Just because you can still play it on playstation isn't the point. How long do you think before those supposed exclusives come to pc.
That point you made of wanting those games being available also works towards pulling folks to other platforms if they know they can play them there. Just having the game on your platform is what Microsoft has been fighting for with Sony exclusives of the past. Microsoft has now used those gaming coming to its platform plus gamepass to make xbox the more desirable platform.