Personally, the comparison makes no sense because the roles are different. And the comparison can't be made at the end of their careers as well. NIko is an entry fragger and monesy is an awper.
You can maybe just gauge the better guy by who plays their role better, instead of gauging their overall impact in a game. Only with this metric, Niko is the better person. And this is just due to experience. m0nesy, for his starting phase in tier 1 is objectively better than many AWPers of his age. And unfortunately, stats aren't the parameter you can look at if you want the answer. Cause perfecto has massive impact as anchor even though he has a poor impact rating. Players like xyp, even in Astralis 2018 didn't have impressive ratings. BUT Xyp's clutch potential and his anchor capabilities helped Astralis immensely
Niko may not always gain entries but that's the problem with any entry fragger. You get naded, get double-peeked, and your pre-aim needs to be 100% correct all the time, which is not possible.
But m0nesy's trade potential is massive. As an AWPer, there's nothing more you want than someone who can almost 100% guarantee you a 1-for-1 trade at a bare