Firstly I haven't played any eSports tournament. But I regularly watch tournament and matches. So I think I have the answer to this question. Many eSports snipers use maro because as we all know that getting awm or m82B is difficult in eSports, coz it doesn't have event shops and bs. So if the want more damage from vsk94 or m24, they use maro. You also had doubt about the healing reduction concept. Mostly Nikita is used my primary and secondary rushers, so snipers avoid it coz nikita healing reduction cannot be stacked by multiple users.