Ehh… I mean. Sure, in the most superficial sense, they are similar because both feature the lavish lives of the 1%. But they’re NOTHING alike in basically every other capacity.

Succession is about how dysfunctional and terrible the Roy family is because of their wealth and privilege, and the draw is in seeing the absurd shit and corporate maneuvering they attempt backfire in their faces. Meanwhile, despite being terrible people, there’s still a very real sense of sympathy for them as people, which is a testament to the casting and performances as much as the writing. They suck, but over time we see why they suck, and while they may have infinitely more than what most of us enjoy, they are maladapted, crippled by insecurities, neurotic.

Honestly, Billions is the worst possible comparison, but if you want a series that is basically the closest comparison, it’s actually another HBO series, The Righteous Gemstones. That series is essentially the megachurch version of Succession, with almost the exact same premise and composition of characters (the presumptuous heir apparent who isn’t the man he believes himself to be, the immature younger brother who clearly struggles with his sexuality, and the sister who fancies herself the clever one, but is just as fucked up as the others, and also has a punching bag husband she takes for granted).

edit: Was on mobile before.

To be clear, while I say Righteous Gemstones is the better comparison to Succession, by no means is it within the context of OP's prompt. Righteous Gemstones is a very good series, that just so happens to share the same premise as Succession. It just happens to go in a wildly different direction (as it should).

Meanwhile, Billions is about the rivalry between two titans of their respective realms, and how far they are willing to go to "win," even after it becomes self-destructive. There's ultimately no "winner," because the story always finds a way to preserve the status quo, and after 5+ seasons, Damian Lewis ultimately leaves the show for deeply personal reasons (the sudden loss of his wife), not because the story ultimately arrives at a conclusion as to who prevails in their rivalry. All throughout this time, while other billionaires may be presented as laughably out of touch with reality, Bobby Axelrod himself is generally treated as a "cool" character; someone many finance bro-types probably aspire to be like. And one wouldn't be able to blame them, because Billions does not attempt to present him as anything other than a demigod with near-supernatural powers of calculation in his ability to see the patterns of the market.

Bobby dresses cool, drives cool cars, and the show's use of "cool" cameos and constant (and I mean CONSTANT) references to pop culture make Bobby seem practically pulled right out of the version of cool-guy masculinity Esquire Magazine tries to sell. He's by no means a satire of wealth and privilege, he's like the young, Steve McQueen-version of Logan Roy from Succession, since both are meant to be the level-headed, intelligent sharks who arose from poverty to become titans of industry.

I'm sorry, they're just not comparable and have completely different themes, motifs, characters, and storylines.