Boring answer, but the one thing I would keep is the source-of-truth content board, not the scheduler. The scheduler saves time at the end, but the board prevents the daily chaos before anything is ready to post.
For me that means one place with the idea, channel, status, caption draft, asset link, owner, approval notes, publish date, and the reason the post exists. If that is clean, you can survive a mediocre scheduling tool or even native posting for a while. If that is messy, every scheduler just becomes a prettier way to lose context.
The test I like is: if someone else had to take over tomorrow, could they tell what is ready, what is waiting on approval, what needs design, and what already went live without asking three people? If yes, that is the tool I would not drop.