You can be very demanding, sure. I'd say it's quite demanding to ask of Flick to deliver 2 titles in 3 years or something like that, or to go very far in CL.
The team is not there yet. If he does something like that, I think he is above good and into great territory already.
It depends on the strength of Madrid. I think as long as we don't have any more awful injuries to important players this squad (when fully or mostly fit) should be able to aim for around 90 points under a good manager, which is usually enough to win LaLiga. That would be classed as a success.
If that isn't enough, I can't blame him that much.
What wouldn't be acceptable however is if Madrid win the league whilst playing poorly and not having that many points. From very very early indications, it doesn't look like they are a points machine this season as they were last season.
CL is very dependent on the draw, we will see what happens there, but in general assuming we don't draw a big fish immediately we should go to minimum QF.
Of course, if he wins the title, that would put him into good territory already, then maybe great depending on context and other competitions.