This is again taking some problems unrelated to Agile and assigning it to it.

“customer is always right” mentality is associated with Agile same as you associate everything else here, it doesn’t come from Agile teaching or manifesto, it’s you misrepresenting one sentence of “collaboration over negotiation” which is merely to not have endless contract negotiations over every single change which destroys delivery and satisfaction, both of customer, company and development team, resulting in project failures.

If your product owner is accepting every single customer request and team cannot cope with it you need to adapt as team to see how to make that working, as simple as that. No Agile is forcing this. It is considered better to deliver smaller chunks and get feedback for future direction than develop mindlessly for years just to fail with a project full of features nobody needs. It still doesn’t say you should develop 1 feature per sprint or 20 or how much you should document or not. It should be what works for your client, company and team. And if you have your product roadmap and features defined fully in advance, then go Waterfall.

That is again what I see wrongly in rest of your proposal. It inherently forces that there is a manager telling team what to do, “allocating a percentage of worker time to documentation and maintenance”, which is exactly what software development industry is moving from.

This has to come from development team, and they are exactly free to do it in Agile.

Also look up “development team” in Agile, it’s not what you think it is.