Suju members get a bad rep and in many cases it is definitely warranted, but Heechul is one of the most loved and respected idols around with a super clean image. To the point most agencies or female idols themselves feel extremely comfortable around him. He's the last person I'd say was predatory or took advantage of Momo. Momo is a grown woman, some Onces need to stop babying her and think they can make better decisions for her personal life.
And a 13 year age gap in celebrity world is nothing really. It's not a case like YG and his wife.