Corporate ownership, but you can have that and still be generally accepted in the community. Like both Fedora when controlled by Red Hat and Suse when controlled by Novell.
One of the real problem is their dual license policy for their open source projects, that grant Ubuntu full license and the power to close in an Open source Project if they want. This is decidedly against the GPL spirit, but can be done with dual licensing.
Another problem is the "not made here" mentality, which undermined Wayland for instance.
Ultimately the problem is I guess, that Ubuntu is (was?) trying to make Ubuntu exclusive to Linux, with Canonical controlling key technologies. Seemingly an effort to reduce other Linux distros to second rate players.
Another example of that (apart from dual license and Mir) is their new package system Snap, which is open source on the client side, but proprietary on the server side.
Obviously it's not a good idea for Linux to use proprietary package systems.

These are of course ideological issues, if you don't give a shit about those, I suppose Ubuntu is mostly OK. Except minor annoyances like media not working out of the box. And that the PPA system sucks.