The way that the system currently favours accepted answers is appropriate.
The asker should wield ultimate, unilateral, permanent power over whether a specific answer should be stuck in the top position on the page, even if the community votes in greater favour of a non-accepted answer.
Unpinning the accepted answer allows better content to potentially occupy the top ranked position. This is beneficial when newer/later answers are posted which are superior to older/earlier answers with the green tick.
Also, because the asker may not be the best judge of which answer is "best", unpinning gives the community the power to ...