The District Courts are one step below the Supreme Court.
There are two, but who’s counting? The step in between is the United States Court of Appeals.
The Supreme Court is materially different because there are but nine justices total (as opposed to 678 District Court judges and around 200 Court of Appeal judges) but mostly because the Supreme Court is the final arbiter. It is the one and only court whose decisions are binding on all those other courts and judges below it.
It’s manifestly different character was recognized when the Democrats did the far lesser “nuclear option” by excluding the Supreme Court from that option. If it were no big deal, or no different, as you wrongly suggest there would have been no reason to do that.