I think the break point was around the release of D7000 (APS-C) which suddenly matched (and surpassed in dynamic range) the immensely popular 5D Mk II (FF), the default choice of videographers and fashion/wedding photographers. Around that time 5D Mk II (and to some extent 1D) dominated.
Only starting in 2010-2011 did they stagnate in image quality for a time.