I don't think you understand the nuances to the game that inhibit the ability of an IGL, and because of that I will try my best to explain why I think your position on FNS' IGLing capability is disingenuous and largely incorrect.
The main points I will specify in my argument is generally inclusive of 4 main things:
-IGL's are NOT always emotional leaders
-The BEST IGL's have always had star talent on their rosters
-IGL's cannot fix underperformance within the game itself
-A team "gelling" is the majority of a coach and management issue
IGL's are not always emotional leaders: I think that you misinterpret what the "leading" aspect of an IGL is; an IGL is meant to call the strats of a game, mid round a game, and instill the structure that their coach or (depending on the IGL) the structure that they want within the game. This is the bare minimum, of course, and while a traditional leader or team captain would generally be the hype man or the "glue guy", this is not always the case and most of the time it isn't.
Take JohnQT and Ange1, both IGL's that are heavily reliant on outside structure that helps them lead their team. JohnQT has Zellsis, Ange1 has/had Ardiis. These players are your people people; the players that "bring everyone on the same page". When a team is built with this structure, it is meant to relieve active duties from the leader and promote stronger team play. Teams like Copenhagen FPX, LA PRX and EG, and Madrid SEN are teams that are known for being well coordinated; being good teams that are reliant on things such as ability combinations and team play throughout the midround in order to win games.
FNS was generally this player for OPTIC afaik, being the centerpiece from which the calling was built off, and while one may believe that this meant that he relied on a lot of firepower from his players, what I believe he actually was strong with was the veteran experience of each player. FNS credits all of the OPTIC members for having provided ample strength within his midrounding and providing strong comms throughout his games; and having their CS experience with them, each of the players were able to play under immense pressure, as shown by their 2022 run.
What an IGL thrives under does not make them lesser of an IGL; Saadhak works best with rookies with strong mechanics; Boaster loves midrounding into or with set plays; Boostio played for team fights across the map; Gambit's Redgar relied heavily on their strong protocols and lurks; and for FNS, it was working off a veteran team and setting them up to be the best players they could be. All of these IGL's lack in something, but they are all considered the best IGL's to touch VALORANT.
The best IGL's have always had star talent on their rosters: I mean this is pretty self explanatory. Every IGL relies on their players being in insane form; Saadhak relied/relies heavily on the fragging of Less, Cauanzin (and previously), Aspas to set up the team for wins, and has shown to want to lean into the strengths of these fraggers in order to make them the best players they can be (putting Aspas on perma jett, putting less on perma viper, putting cauanzin on perma breach). This follows suit to other teams: Boostio and EG, PRX as a whole, Gambit with nAts and Chronicle, Acend with cNed and Zeek, hell even Reykjavik 2021 with TenZ and Sick being insane fraggers. I don't understand how FNS should be knocked from being one of the best because he "need[ed] the firepower of peak yay and peak marved". You could say the same about any of these teams and their star players.
IGL's cannot fix underperformance within the game itself: This is a very specific point that I want to make, but I think it is important. Many people see a player underperforming and can immediately think of many reasons as to WHY a player would be underperforming. Pressure? Maybe they haven't ever touched a LAN before, maybe the team is just underprepared, maybe their supports aren't helping them enough, but an IGL can't focus on that in the middle of the round. Nothing FNS can say, besides putting ardiis in advantageous positions (which he would often start the round in) can change this issue, nor should it be FNS' issue in the first place. The structure of Optic and NRG have long been known by this community: methodical gameplay with strong communication into a strong site hit or read from FNS. This structure is built off of the individual and the information a player can gather within a game, which is something that not a lot of people realize. This clearly did not fit Ardiis' gameplay style, and while that is not his fault, it also is not FNS' fault; and Ardiis not being able to play within their system does not make FNS a bad IGL.
A team "gelling" is mostly a coach and management issue: I also believe this one is pretty straight forward, but a team should not be having issues "gelling" at the end of the season when they had plenty of preparation time. The fact that this is a slight against FNS is crazy to me, because Ardiis had plenty of time on NRG and if their coordination was off, that is what the coach is there for. Team coordination can't be fixed mid game, that is something coaches and staff work on with their players, that is what scrims are meant for; and if they feel Ardiis was not a fit for the team, that is management's issue.
I think calling FNS a bad IGL because he lost to BilliBilli is deceptive at best; that team was falling apart and there was clearly not much that was able to be done by the players or staff. They lost, and yet every player that was on that team is still exceptional and worthy of praise, while also being some of the most decorated players that have touched this game.