Not GP, but it matches my experience: with reverse DNS, DKIM, SPF, being in DNSWL (and not in DNSBLs) some of my messages end up in Gmail spam folders (very recently received a reply to a message I sent 3 years ago because of that, for instance). A while ago there were strange issues with Google-hosted mailing lists as well, with some messages not being visible even to an ML administrator, while Gmail servers accepted mail just fine (maybe it still happens, I'm just not writing to those). I hear similar stories from other mail server administrators too.

I think it's more of a Gmail/BigMailerCorp issue, and still using a private mail server myself, but I don't think it's fair to say that it's all easy and works flawlessly, even with strangely behaving mail servers on the other end.