I'm not really sure why "fragmentation" is still an argument when referring to Linux, really.
If I were in the position of making the decision about porting a product (game) to Linux, here's what I would see:
Ubuntu is the most popular desktop distribution. It is backed by a for-profit company which aims to bring the Ubuntu distribution into the mainstream. Ubuntu has a long-term support release which backports new features related to graphics drivers and hardware support (therefore "fast release cycle" is a moot argument). Along with its huge number of users, this distro also has notable derivatives such as Linux Mint which are fully compatible with Ubuntu. Supporting Ubuntu will support a large chunk of the Linux community.
Fedora is another large distribution with a huge following. Supporting the latest release (or previous) would be harder than Ubuntu, but would only require more work. Supporting Fedora would make it easier to support RHEL (and other EL distributions such as CentOS, Scientific Linux, ROSA, etc).
Users of Arch (or other "advanced" distros) don't really require hand-holding. Chances are, someone within the community will add Arch-specific packages to AUR or write a guide to make it work.
Granted I'm not that familiar with the process in which considerations are made for porting to other platforms, but I don't really understand the "fragmentation" argument. Is it really so hard to decide that supporting Ubuntu (the most used desktop family) instead of Slackware or Yggdrasil is a more logical option?