We haven't cruised on Oceania, but from what I have read and heard first-hand your suspicions are well founded. Fellow cruisers on Regent who have also cruised on Oceania feel Regent's food is better.
We enjoy the entertainment on Regent, but it's closer to what you describe on Oceania than what might be available on lines such at Celebrity. There are lounges with entertainment as well as a main stage with well done shows.
Our second cruise experience on Celebrity was 55 days on the Edge in the Med and a TA. We enjoyed an excellent time in the Retreat. The food was mostly excellent and the entertainment was top notch. As mentioned above, we're on the Ascent for a TA in October. If you haven't reached final payment for your Oceania cruise, I strongly suggest you give one of Celebrity's Edge class ships a close look. There are some good videos on YouTube you might want to check out.