Data point:
Just got approved for the personal Marriott 80K. In the last 24 months, I have opened 1 personal and 3 Biz from Chase (UA, Marriott Biz, UA Biz, and Ink Plus). Last app was in September 2014. I have also opened another 16 accounts (most have been closed) from other banks (mainly Citi and AMEX) in the last 24 months. This Marriott was auto-approved. I also applied for th Citi AA and that app went into further review mode (I never call). Last app before this mini AOR was on July 28 for the Wyndham Rewards CC (auto-approved).