It's not just research published in journals. Siri was largely developed by the government, for example. There's a lot of tech transfer. The people who work on these projects with taxpayer funds go on to start U.S. companies or work for them. The U.S. also spends billions on procurement that's only for nascent U.S. companies while they bring tech to market.
The claim wasn't that SV tech is successful because hiring is easy. The tenure system shows that easy firing isn't essential to successful tech innovation.
Some govt research is directly given to a particular valley company and no one else, but quite a lot of it is published and free for anyone in the world to use.
As for the tenure system, firing is hard and as a result getting hired is also extremely hard.