How is it suitable that the harsh permanent penalty is given to the sinners in the hereafter, where the sins…

Answer

In the name of Allah, be advised, my son, the ugliness of the sin cannot be measured with the period, but with the ugliness of the sin and the ugliness of the consequences. One may take over a house and live in it for a thousand years and may kill a person in a moment. Does your reason judge that residing in that house is uglier than killing the person in a moment? Furthermore, there are some narrations about Ahlulbait (PBUH) saying that the sinner is permanently thrown in the hell only because he insisted on his sin throughout all his life. So, his staying in hell for good is a result of his insistence rather than the duration of his sin.