It turns out that an important soft skill is knowing how to make these kinds of drafts work in your favor, especially with internal stakeholders, by doing drafts that are annotated with where you want help and input.
As one example, "We want to work on the foobar because [get exact wording from team] to improve throughput [%]. We will request [#] team members for the next [n] months. We're working on decision records for our top 3 options which are [1, 2, 3]." Share these one-on-one with each stakeholder, gather feedback, and hone the draft.
For technical work as described in the post as "write a technical spec for engineers in & outside of my team", I recommend trying an architecture decision record, and sharing drafts early/often with stakeholders.
https://github.com/joelparkerhenderson/architecture-decision...