Of course summer is a time of slow sales. But year-on-year comparisons to past summer months are not encouraging. I do not like the trend here: a big reason why PS4 and XBO are ahead of the previous gen is how front-loaded the sales were.
Having said all that, of course Holiday seasons are the real acid test for this generation. If they do gangbusters during Christmas period, all is well. If there is sustained year-on-year drop there too, it is time to get worried.