I mean, it’s a lot. Certainly the majority of regular contributors. Probably 80-100ish full time employees working solely on WordPress OSS projects. (Some in community roles, executive director, tech leads, devs, designers, etc.) There are certainly other regular contributors (Yoast sponsors a couple people to work full time), and lots of volunteers. But without question, Automattic spends a lot of developer time on WP.
And in other parts of the business, there is a strong desire to “fix it in core,” so if WordPress.com wants easier site building for customers, well hey, send devs to help build full site editing in WordPress.