Because annoying 2 hour installations with 7 patches are a thing of the past due to Steam, for the most part, which is a big reason people love Steam.
I guess I should have started a "This is why people love GOG (and hate Steam)..." thread a couple of days ago, when an automatic Steam client update gone awry made all my Steam games inaccessible for me. But since I considered it an individual incident, I merely mentioned it in the discussion where someone else was venting about a similar incident.
So these clients or games have occasionally hiccups, nothing new under the sun. If many UPlay games start having issues like you described, then I guess there is real reason for concern. Yeah, patches should include also earlier fixes so that installing only the latest patch is enough.
But to even things around a bit, I'll also use this opportunity to complain about a recent and persistent hiccup with EA Origin. Namely, it seemed that whenever I tried to start Crysis 3 MP beta, it would just crash. The only way to make it work would be first to tell Origin to check/fix the Crysis 3 beta installation. It would check the installation for a minute or two and report "no issues found", but only after that the game would start ok. So I had to repeat this every time I wanted to launch the game.
I am unsure if that was some kind of generic problem with Origin or just a Crysis 3 beta issue, but I was a bit surprised they never seemed to fix it in the beta (ok, maybe beta was just one frozen test version that didn't even receive updates... whatever).