IGLs

what role does the igl play most commonly?

idk

Controller , Initiator , Sentinel , Duelist

I'd say it's not a fix rule thing but it's mostly anything except duelist?

to give calls, guide the team plays and help out usually the star frag or the entry fragger, maintaining the metal of the team

Usually Sentinel from what I’ve seen

I was going to make a pie chart from notable NA+EMEA+APAC teams (BR+LATAM omitted due to me not knowing much about those regions) but got bored half way through. I looked at about 20 teams and would estimate it was around 40% controller, 25% sentinel, 25% initiator and 10% duelist.