So, in your realistic use case, you can't think of any reason to get an Apple TV 4K over Roku Ultra?
That would be my thought too, with the exception of Infuse native playback of any format without transcoding on Plex. Also, Siri and Apple Home Automation can use Apple TV as a hub, but there is virtually no hardware support, or they are way to expensive over the competitors. Then, maybe privacy and security of Apple software over Android, etc.
I'm really debating if I should just get Roku Ultra instead.
I'm not a fan of either Roku's or Apple TV's interfaces. They both have app-centric interfaces which (IMO) is not the right approach for TV. I just happen to use Roku because it's built into my TV and it's easy enough to launch AirPlay or my Fire Stick. Roku's app ecosystem, quite frankly, sucks. Roku is using a custom Linux build, not Android, so privacy/security is similar for the Apple TV and Roku.
You're probably better off going with a retailer that will let you try both for a few weeks and then decide. You may be happier with Apple TV because of the better App ecosystem. Sorry for not being definitive but it's highly subjective.
But if you're comparing Fire TV or Android TV to Apple TV, the Apple TV would lose almost every time. These devices are just much better at discovering new/related content.