Perhaps, but as they say, credibility doesn't pay the rent. What matters in commercial terms of how much money the book ends up putting in your pocket.
If a publisher is keeping 90% of the revenue, the services they offer had better generate at least an order of magnitude more sales to break even, less anything it would have cost you to obtain any other relevant services they provided directly instead. Does anyone here believe that this is in fact the case with the level of marketing that a typical tech publisher will do for a new work from a previously unknown author?
The goal is not to write a book that directly makes money. The goal is to write a book that gets the author hired or promoted, or to land consulting gigs, or to get VC backing.
So, yes, credibility does pay the rent.
Agree on the minimum wage comment, though. I did it for career progression, personal life goals, and passive income.
[I assume you can write and organize thoughts decently well, and have some people who can proofread for you. If not, a publisher really won't help too much with that anyway.]
So what does a publisher provide? Marketing, promotion, distribution, reputation. No matter how good of a book you write, having a name publisher like O'Reilly gives you substantial credibility that nothing else will. They can arrange promotions through conferences and email distribution that you probably can't. I wouldn't underestimate this, but I also wouldn't necessarily think it's worth their 80%-90% cut either.