Questions that, essentially, bring a site-specific matter from another site here looking for support and affirmation are poor questions that should be closed. That's true whether the other site is an SE community, a subreddit, or the unicorn-lovers mailing list. (This is not an exhaustive list.)
Questions that ask what you can do about problems you encountered on other sites, including SE, are just as on-topic as questions about problems you encountered with your family, coworkers, bowling league, or place of worship. (This is not an exhaustive list.)
Robert's post, as I read it, says that we should close those questions because they belong on site-specific metas or Meta.SE. But "fits better on another site" is not a valid reason to close a question. As Shog9 wrote in Respect the community --
your own, and others':
As members of a community, your first loyalty should be to that community. When evaluating a question, you shouldn’t be looking to push it off on some other site; instead, ask if it could be appropriate and on-topic for you, the experts who the author decided to ask. Be a bit jealous of your site – don’t blithely turn askers away simply because their question could be asked somewhere else. Don’t hit them over the head with your scope, help them tailor their question to fit into it – and if that means your site’s scope overlaps a bit with another site’s, so be it.
IPS is not the first site to have this kind of overlap. Community Building also covers questions about things that happen in Stack Exchange communities, such as:
All of these questions could be asked on metas. Some of them probably have been. Asking on Community Building invites answers from a broader perspective, which can be valuable -- experiences of dealing with people and shared content and abusive behavior and other issues transcend platform. So long as the questions aren't "solve this problem I'm having on Server Fault", it's fine.
And all of that is true for interpersonal communications, too. A question can gain valuable answers from people who've never used any other SE site but who have other relevant experience. The focus with these questions, on both CB and IPS, is "community (or people) first, SE second". On Meta.SE and the child metas, on the other hand, it's usually the reverse -- the SE network and its mechanics, policies, and history are front and center, and answers that drift too far away from that will not fare well.
Don't treat IPS as your out-of-band appeal channel for that argument you're having over on Unicorns.SE. Don't treat it as a substitute for using meta -- your site's, and MSE -- to resolve differences. But some questions are less about the specific issue and more about a general situation, and we should welcome those without demanding that askers first file off the serial numbers. (Provided, of course, that they meet our other criteria -- "good subjective", not too broad, etc.)
A postscript: IPS is a Stack Exchange community, and Stack Exchange always has the final word. If they don't want a certain type of content on a site, then the site won't have that content. I don't think Robert's post is SE policy or I wouldn't have bothered to post this. SE employees are also sometimes users, and I'm assuming that's the case here. (Granted, this user also has mod powers.)