So we all now realize that the reason there's no Doctor Who this year is because of Class, right?
Correlation does not imply causation. The existence of Torchwood and The Sarah Jane Adventures didn't keep Doctor Who from coming out in the same years. Class has a different writing staff, it's aimed at a different age group, and it's aired on a different channel, BBC Three instead of BBC One. So there's no reason it and Doctor Who couldn't coexist.
According to the BBC press release, the professed reason for not having new Doctor Who in 2016 (other than the Christmas special) was to avoid competing with major events of the year such as the Olympics and a major European football/soccer championship. Since Series 10 is Moffat's swan song, they say they wanted it to be a big event free from other distractions. Other sources suggest that the delay is to accommodate Moffat's Sherlock schedule, so that he doesn't have to rush the writing of Series 10 and can take the time he needs to do it well.