Good. That's the point.
I hope they fixed phabricator in the meantime.
One merged pr is a unit of change, at the end of the day the steps you took to produce it aren't relevant to others.
My opinion of course, I'm open to understanding why preserving individual commits is beneficial
See how the Linux kernel handles git history to see a good example of non-linear history and where it helps. They use merge commits, ie commits with more than one ancestor, all the time.