so when @aggroed want vote with his stake why he bring them to hive-engine and not to his own account

I have no idea, this is a good question for @aggroed

the border to accept a proposal from 66.67% to 75% so that really a majority of the player should be behind the proposal and not only the whales. How about this suggestion ?

That's a fine suggestion, but it's not for me to decide. You can feel free to submit a proposal for this change for a governance vote.