I'm on a PC with the Chrome browser and I was just not able to log into Rakuten, find QVC with a 1% cash back offer, and launch the QVC page from the Rakuten site.
I tested it on Safari on my iPhone and was able to visit Rakuten in the Safari browser (I have never downloaded their app), find QVC, and click the button to launch QVC. From there, it opened QVC in Safari and forced me to the QVC app, but it never sent me back. It looks like if I had not had the QVC app on my phone, the site would have forced me to download it to use Rakuten, which is a big negative from me.
Also, Mr Rebates has 3% cash back now. It also forced the app open instead of Safari, which is new behavior as of this week. I used it over the weekend and it did not force me to the app.