It doesn't seem that way to me, e.g. Putin arrested Khodorkovsky (the richest man in Russia) in 2003. The way I see it, the politician needs the oligarch's money to gain political power, but then he has actual state power, including guns and the judicial system. At that point the oligarch has no purpose -- after all, the politician can just make new ones -- so it makes sense to cast him out or destroy him.
Trump could bankrupt SpaceX with the stroke of a pen and bleed Tesla dry by revoking EV credits. He could even try to revoke Musk's citizenship over (real or fake) issues with his immigration status in the past. If Elon thought he was buying the presidency in exchange for favors, he wasn't thinking things through.