RE: So the question is what happens if powerhouse with 1 000 000 SP powers down?

You must learn about voting power:

You can see your voting power below on steemd.
Is kinda distributed like you said but in other fashion. With something called V-shares and R-shares i but this is bit technical and oudated too, but can help you a bit.

In post above i try to explain what happens with ecosystem when poweringdown of powerhouse is going on.
Here are some nice stats about anyone you can change @ part withsomeone elses name

And mandatory for understanding how thing here wotk is by reading whitepaper explanations its lenghty and technical but has some graphis explanation to understand how it all works.
https://steemit.com/steem/@tuck-fheman/how-is-voting-power-determined-in-steem https://steemit.com/theoretical/@theoretical/the-steem-reward-system-part-1-v-shares https://steemd.com/@leksimus https://steemit.com/steem/@liondani/steem-whitepaper-download