Experience: Hello! I IGL for a tier 2.5 team, Ive also watched VCT for 4 years, I believe I can give some insight.
https://tracker.gg/valorant/premier/teams/dee29c91-7b1f-4ac7-87c0-6685d504c7d0/overview
I peaked IMMO 2 156 RR https://tracker.gg/valorant/premier/teams/dee29c91-7b1f-4ac7-87c0-6685d504c7d0/overview, Ive played against the best teams in OCE albeit losing and participated in many tournaments (notably not VLR ones). And ive also played against some tier 1 pros before.
Now on Average I have a 311 tracker score in prem. And I usually am either +1, +2 or negative, there are times I do well, but its not the average, and I have absolutely had tragic -15 games.
Actual take: It really depends on the teams system. Its all about the what you are doing on IGL, and how do you set the team up to do well. on my team for example, we hard set up duelists, they are 90% of where the utility is going towards and have the highest chance of getting favoured fights. So the only kills im getting are clutch kills with low utility or trades. Other teams may differ, such as TL often set nAts up with game winning lurks, or TH who are a trade heavy team famously sending miniboo in like a drone.
For teams that have heavy fragging IGL's they play around that, and the system sets them up to frag, for G2 its the team fights they do and the trades they set up, for TL or EDG its nAts or nobody lurking and trading teammates. Etc etc. For teams like fnatic where everyone is being set up but boaster, its expected for him to go negative, if he isnt going negative, he is either having a life game, or the enemy just isnt that good. boaster is sacrificing his fragging with calling. the spots he is in, are often not favoured for him, as most "easy duels" are set up for kajaak and alfa.
Different systems are not better than others, some teams do really well with fragging igls, some teams do really well with non fragging igls. the system bends around the players you have, you dont force the players to bend around the system. Obviously there are caviets, going quad neg in a game is terrible, and require you as an IGL to be making the perfect calls and have the 4 players on your team be better than the enemy. but overall It is often okay for IGL's to go negative and still for them to have a majority positive impact. Being an IGL means you focus a lot of your awareness on everything but the game.
A team like fnatic, would never go that far with a player like Valyn or Nats, if they stuck to the same system. Going Neutral for an IGL is like the perfect spot you want to be in for most teams. as that is the most common system for teams to play towards