You don't seem to see how fragile all of this is. Debian is not invulnerable. Just because "half of Linux", most of which has no abundance on volunteer workforce, either, relies on Debian, that doesn't mean Debian couldn't die anytime soon. And the least bad outcome, if it actually did, probably would be a commercial takeover by one or more of the corporate entities that rely on Debian or derivatives of it, a takeover which would have to be crafted very carefully to not become as bad as it sounds, to not completely change what Debian has been so far.
As to your last sentence, I would mostly agree, but maybe say they did not properly forecast the level of work Canonical Corp. would impose on them by things they forced upon Ubuntu.