It's a bulk of an entire character, not any player character.
The difference between a champion and a multi-caster is pretty significant, but there's no reason why any non-player character should approach even the complexity of a champion. We're literally talking about a character that doesn't have a player. Nobody benefits from it having more complexity than is absolutely necessary. Complexity only adds to the difficulty of the DM running the character, on top of everything else they have to do.
I can see you're not listening (which is fine, this is a public forum), but since other people get to read this, I'll put it another way for their benefit.
A champion fighter of any given level fits into a 3x5 card or less. There is no difference in complexity between running it, or a hobgoblin, for instance.
The fact a champion can be played by someone at your table has zero weight gauging its complexity, much like any creature from the monster manual. You could easily have a table of players running creatures from the monster manual; it wouldn't have any bearing on whether the statblock could be considered complex.
The complexity of the statblock can be placed on a low-high scale based on I think are some good measurements:
- How many different possible actions does the creature have?
- Can it use more than 1 in a given turn?
- Does it have to frequently compare a variety of actions to use? Or is there a clear default?
- Does it have any interrupts (things it can do on other creatures' turns)?
- If so, how many?
- How many rolls does it take to adjudicate what those interrupts do?
- Can the creature inflict status effects?
There are doubtless more, but these are the few I could come up with off the top of my head.
The champion places "Low" on all of them.