It's easy to "manage open source perfectly fine" if you just open-source less of your code, or release it without any patent grant at all. I'm not sure how much credit should be given for those non-efforts, though.
There are plenty of reasons that someone might choose not to open source code (e.g. they like working on only internal infrastructure or don't want to bother with external maintenance), but I don't think the patent grant has anything to do with why a developer at {Google, Facebook, Microsoft} would choose to open source (or not) a library.
The whole process is documented here (https://opensource.google.com/docs/releasing/approval/) but here's the tl;dr:
1. Googler tells their director that they want to open source some code; the director approves it.
2. Googler tells the Open Source + Patents Office that they're releasing code. The OSPO says to use Apache as the license unless you have a good reason not to, and does a sanity check to ensure that the license information is in all the right places in the repo.
3. Googler posts the repo to GitHub.
Googlers don't usually even think about licenses. The OSPO says to use Apache, so that's what we use.
What about Google and Microsoft's FOSS contributions do you consider "non-efforts"?
It's not the FOSS contributions that are non-efforts. It's the things that were never released at all. What percentage of engineers at Microsoft work on code that has been or ever will be open source? How is releasing 10% of your code with no patent grant better than releasing 20% of your code with a conditional one?
Also, "no explicit patent grant has been sufficient" is no excuse for bashing a grant that has exactly that as its worst case. Any non-zero protection is still greater than zero. By way of analogy, would you yell at people on your team who you felt weren't working hard enough, then give a big pat on the back to one who played video games the whole time? Well, maybe you would, but an objective observer might think it seemed unfair. They might even wonder about what other motivations might be involved.
* Release lots of software with a conditional patent grant: awful.
* Release lots of software with no grant (e.g. BSD): OK.
* Release very little software, and that under the no-grant license (e.g. MS): you rock.
Sorry, but that's completely f-ing backward. It's literally impossible to get to there from open-source principles, so what what principles are people starting from?
It's true that, practically, most companies won't ever have to worry about Facebook infringing their patents, but I think it's garbage on principle to reserve first-strike litigation while making it impossible for someone else to do the same and use software you've made available under a supposedly permissive license.
That phrase alone should swing the "legal risk" argument the other way that how it's being portrayed here.