There's also The Expanse, Killjoys, and Star Wars: Rebels.
I wasn't counting animation because its not quite the same thing and if I did I'd have to decide if I wanted to include anime (plus Rebels is made for people younger then the general audience to adult level sci fi I'm talking about). I don't consider Killjoys a space opera so much as just a show that takes place in space, so I didn't mention it. As for The Expanse, I forgot about it mostly because I prefer to forget it exists. Plus its more "space simulation" then space opera, and I also really don't count shows that can't get past Mars as a space opera (faster the light travel, even in a small area like Firefly, is also a requirement in my opinion). Its like saying a movie about people driving two blocks to a gas station is a road trip movie. The scale is just too small.
So, as far as I'm concerned, Orville's only competition as a Space Opera show is Discovery and Dark Matter, although I'd hear an argument for Killjoys (I suppressed the bit of that showI suffered through so I don't remember if it did more then be about some bounty hunters traveling between a few planets).
None of those three shows are worth the time, money or resources it takes to make them, but Orville will, in my opinion, be the only one that might be tolerable, at least slightly. To be fair, dark matter season 1 was actually good, which Orville has no chance of being, but DM season 2 was bad enough that Orville can beat DM post season 1 probably as easily as it will beat Discovery.
You do know
@kirk55555 will now tell you that these shows are the absolute worst things humanity has ever produced?! It's what he does.
Well, The Expanse might be close to that, although if we go past TV shows then 2001 A Space Odyssey is the king of shit hard sci fi (by which I mean all hard sci fi, because its all terrible in my opinion). At least the Expanse probably has a story that doesn't take 5 years to actually start and probably doesn't end with complete gibberish. Outside of hard sci fi, Killjoys is also pretty rancid but probably no more so then Dark Matter post Season 1.