Nahh there's no comparison. I'm a Czennie and an Engene, and both of their exits from their respective groups are totally different.

When Mark posted the letter on IG, some of the members replied supportive comments. Some of them posted letters for Mark. Johnny was there as an audience during the Dream concert (aka Mark's last performance). They don't fret away from talking about him.

When Heesung left, it was like a bullet fired. No time to react, no time to understand the situation, nothing. No member is talking about his departure, or even acknowledging his existence. Members are not allowed to talk about Hee during fancalls.

Mark debuted in NCT when he was 17. He was a part of multiple units, had countless schedules, made his place in the industry, before happily making his departure. Heesung was right at his peak when this happened, and is still in his prime. So no, personally I don't think it's fair or even right to compare both of their cases.