Is TinyMCE perfect? Far from it. But it's stable and reliable across browsers, with a well-defined API, and it gets the job done.
I know a lot of folks here would just as soon just use Markdown for all content writing. I like Markdown. Clients hate it. It feels like an obscure language, when they just want something "like Microsoft Word".
And CMS's can hardly say "Yeah, we know we used to support these greater markup sets, but now we're just not going to, so don't open up your old posts, or they're going to lose some content in our bright shiny new editor" -- that's massively problematic as well for user trust.
If you're starting something new, and want to place a hard cap on what your users can do markup-wise, sure, give this a shot. But be very aware of the restrictions that you're imposing.