Support is the biggest issue with open source. It's why companies like RedHat, DataStax, Hortonworks, Databricks, MongoDB have all done so well. They basically took over their open source projects and provided official vendor support in the Oracle "style".
They all offer certifications, training and conferences around the world for you to spend company money on.
For a start, that's why I don't work (at least directly) for the enterprise world.
But I've seen companies adopt open source solutions and modernize. I've also seen companies use those "legacy" technologies. They're the ones that usually go bankrupt, unless technology is a minor part of their business.
And yes, as much as "corporate architecture" is 90% BS and politics, if you can at least explain why solution A is better than solution B in a way it's understood, then you did your part.
And the question remains, who will pick up the phone when an open source DB fails to perform as it should. Does Red Hat provide support in that area?