I get a distinct Flash-bashing troll vibe off this question, but I'll put in my 2 cents:
So is Flash usable as a website
framework at all?
Flash is just a plug in, so this question could be reframed into, "Is [a runtime object with access to JavaScript] usable as a website framework at all?"
The answer is yes.
With an understanding of the plug in and its relationship to the browser, most conventions from non-flash sites can be replicated in Flash. Google actually spells out how to solve most of your questions, if you read the pages you link to.
The question of whether Flash can play nice with SEO has been answered in commercial apps. I know because I worked on a few. That said, it takes expertise and effort to make the plug in mimic HTML page behavior.
The current major failure of the Flash plug in is in mobile browsers, but Adobe seems highly motivated to get that working.
Just because Flash sites have been poorly executed hardly means the technology can't support certain use cases. That said, Flash is just a tool. If it makes sense for a site, then use it. If not, then don't.
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For SEO, it's pretty straightforward: use the noscript tag to load the page with HTML content that reflects the flash content. On any decent sized project, the deployment process (or runtime scripts) would automate this task. The assumption is that is the content is important enough for search engines, it is important enough to move through a CMS and be read into Flash and the page dynamically.
For deep linking, you would use ExternalInterface in ActionScript to communicate with the browser JavaScript and read/write content hashes to the URL. This is SOP for any kind of complex Flash or Flex application. Adobe includes an implementation in the Flex SDK.