I had that same feeling up to late August when the backdoor fiasco happened... everyone thought Toonami was in serious danger, but then LOL BebopAirz and it turned out they were actually gaining a half-hour. If the block really was in danger of being cut with ratings like this, it would've already happened. DeMarco is one to tell us when things aren't going to well, like back in early 2015 with the mass block cut. So unless something sketchy is going on behind the scenes, I guess we don't have to worry about it.
Also, the TV industry is not just going from points A to B and having to fight monsters along the way. There are logistics on top of logistics, always more than what we think we know, so anyone who thinks they're an armchair quarterback and can do it better than those at Williams Street is almost always wrong. Who knows what's been going on? Maybe streaming numbers are up for them and the other Turner channels, so they can afford to sink more money into their anime fetish? Or maybe Rick and Morty did so well for the network that everything else is just running up the score? You know, pad other things out to appease the fans.
And going back to my previous point, I probably should've worded that a little better and included something other than the nihilist talking point. Yeah, Toonami probably should be advertised a little better than it is. There was some guerrilla marketing for Samurai Jack S5 that people liked, and I'd guess they do it again for other big projects like the new FLCL seasons, but other than that, the block has been a niche thing since [as] brought it back and I guess the crew wants it to stay that way, especially if the ratings are in fact decent.