It wouldn't have hurt Rafa, even as much as he likes fast Clay conditions now. If Roland Garros played like hamburg that would hurt him, but that would just be stupid. Novak maybe could won 2013,2014 against him on slow clay. Still very doubtful though.
Federer best clay master's Hamburg was actually slower clay. So I have no doubt he'll still have one RG. No difference either way.
He did play well in Hamburg, but Hamburg played the least like a proper Roland Garros court of the 80s and 90s. That court was at times like mud, you didn't slide through much at all, and very low bounce for Clay. Roland Garros was slick high bounce just very slow. Forget the past decade, the almost exact comparison, best indicator historically is Monte Carlo. The exact same clay.
The clay was slightly slower this year, still needs to be better. It's not like the debacle of 2011. Even a few years before that was way too fast.