AU3 is still not a clean, consolidated, properly integrated new feature in Logic Pro. On top of the cumbersome faff involved in setting up AU3 mixer strips and tracks, I've been encountering horrors when dealing with the AU3 client mixer strip's extension into aux audio strips. It's all a bit depressing but I'm still battling on with it - I have to, for now, because I use a huge intonation subsytem I've built in Logic's Environment.
What was previously a masterpiece of real-time software engineering developed by E-Magic, now seems to have fallen victim to Apple's questionable abilities in software app development. (I go back only as far as Logic Audio Platinum 3.5F, and don't know what Notator was like.)
You might indeed do better with Cubase, but a lot depends on whether you're comfortable with Steinberg's long-term marked preference for old-school PC-type functional structure and user-interaction. Recently I bought Cubase as a hedge against Logic's increasing mess - having previously tried and failed to get along with Cubase back in 2001. Although Steinberg have been trying hard to move Cubase towards today's more slick, glamorous and intuitive styles in music production software, I'm finding that learning Cubase Pro 11 involves me in something akin to a change of religion, lol. (I've been commited exclusively to Macs since 1984.) However, I'm now pretty confident that Cubase is a hugely capable and thoroughly professional DAW. One day I'll probably dump the ever more amateurish and bug-afflicted Logic and become a full-on Cubase user.