I don't see it in tech circles as much, but in other circles like consulting, banking, advertising, it's pretty common to see people constantly cycle back and forth between the same set of employers every couple of years. Think Goldman Sachs trader leaves for JP Morgan, then leaves for Morgan Stanley, then leaves for Goldman Sachs, and so on
The idea that senior engineers need public commits to be even considered for a job seems a little extreme to me. There are myriad reasons why an extremely competent senior engineer might not have public commits.
The lack of public commits does not signal whether or not someone is a competent senior engineer.
Yes, this does happen. Especially for HR related matters. But that's definitely more of an exception than the rule. For most services that I use on a day-to-day basis, the experience is seamless.
My experience is completely opposite of the author's. I sign on once a day when I access a service that uses my firm's SSO solution. I'm then automatically signed in to all other services as I use them. It's quite seamless. I have no complaints about the SSO setup in my firm.
Web development is the way things are moving - a lot of "desktop" apps now are web apps in disguise (thanks electron). It's worth getting familiar with web development for the job opportunities alone.
It always (still?) surprises me how difficult it is to share files across the Internet. You'd think this would have been a solved problem already given how long we've been communicating with each other electronically.