Sorry for longest answer in HLTV history
I do agree with you to some extent. You can also see that they actually had more stable and somewhat better results with Zews as a standin than they did with Coldzera. I could, and might later on, do a 40 min long video explaining this into more details why they looked better with a 10k playing Zews than with a 30 bomb dropping Coldzera.
But lets start with the claim that FalleN is outdated/obsolete with his gamestyle as an IGL. It is somewhat true, based on how simplified his defaults and executes are and how performance heavy his calling is. It isn't really reactive nor proactive. He just set up some basics and then let the team run off of it. So I agree with you there.
When it comes to their 4th & 5th player rotation the reason it hasn't worked is either due to personality reasons (FNX and Boltz) or because of role slotting (Brax/Swag, Tarik, Stewie2k, kNgV, Lucas1...)
This is due to their core lineup, whether it consist of Taco or not, is based of their slotting but as they grew as a team together they also incorporated a hierarchy that isn't healthy for the team, if they want star players/aimers joining the team. This is the reason why I go with a young role player instead of a roleplayer from Furia, ex-INTZ, ex-Luminosity etc...
When FalleN and Dead created this roster the hierarchy was simple: 1) FalleN, 2) Coldzera, 3) Fer, 4) FNX & 5) Taco (I count this from 2015-11-23 when Taco and FNX joined, and not the Steel and Boltz lineup). When you remove FNX Taco had proven himself within this team and therefore climbed the ranks to FNX spot. So it was quite simple to add Felps instead of FNX, similar play styles, not as huge ego and therefore he could come in and play bitch role and be 5th in the hierarchy. You could also see that they kept on winning events after this roster change, so the team dynamics seemed to work.
Then for some reason, this happened when I just started playing and watching CSGO so I am a bit uncertain of what happened when, but there were internal struggles within the team in early 2018 and players became unhappy. Contracts were close to expiring and each player had to make a huge decision by themselves: either commit to the project or find success elsewhere. Rumors about SK wanting to create a new FaZe roster (S1mple rumored), took a toll on Taco who most likely felt he was on the chopping block, since the hierarchy is more important than the role slotting in FalleN's and Dead's team.
Taco started looking for a new project and after a long back and forth discussion with multiple players SK took in Stewie2k. It had also been months with a variety of standins for Felps/Boltz spot.
But how do you slot in Stewie2k (recently a Major winner) to play instead of Taco? Where do you put him into the hierarchy? He came in and had to play bitch role and 4th in the team, but was an international superstar. This is where the roster really started to crumble (ok, the standins was the first issue).
They move the project to MIBR/Immortals and add Tarik. How is the hierarchy now? They have 3 different callers in the team (Coldzera had recently called due to some bad results during the stand-in period), they had no real entry fragger, no real support player, and no real entry fragger. What they had was 5 individually gifter players where they either played mid-man or lurk player. The most unbalanced team in the history of CSGO, including FaZe clan after Karrigan left.
The hierarchy was in shambles but tried to remain: 1) FalleN, 2) Coldzera, 3) Fer, 4) Tarik, 5) Stewie2k. But Coldzera had been top of the world for years now and started to see himself as more valuable than FalleN.
So the hierarchy that had built them this great era (even though it was short) had been tilted and shifted by time, while the calling and strats became less important (also due to lack of role players).
So Stewie2k left, Taco came back, Tarik left and Felps came back. So now the order should be restored right? This was the roster that most recently was a success story back in SK. But the weird thing is that Fer's individual performance had dropped, so he should've been 5th player, Coldzera and FalleN still argued who was 1st (not literally argued) and Taco should've been 3rd but because of the weird exit from 8 months prior he and Felps shared 4th spot.
The team dynamics was in shambles and just became more and more obvious to be a disaster.
The team didn't work out, and they blamed Felps, due to his CT-side being bad and his calling lacking (each stand-in and player during this whole decline had pin pointing calling being a huge issue within the team, no matter if it was English or Portuguese). So without thinking why Felps wasn't playing as the rest of the team, which was due to bickering within the team and FalleN not being as good IGL as earlier, he had to leave. This is also a time where Zews has come back and taken over/lighten the burden of FalleN, which actually seem to have a negative effect on him (yNK had the same effect on the team).
They brought in the best BR player they could find, Lucas1. But where do you slot him? He most resembles Fer in playstyle, but have to play the FNX and Felps role, while they downgraded Taco to 5th and let Lucas1 be 4th.
In reality it should've been 1) FalleN, 2) Coldzera, 3) Taco, 4) Lucas1 and 5) Fer. That would've avoided 1 of the 3 issues, the other two being slotting and calling. But the actual hierarchy was divided between FalleN's POV and Coldzera's POV. where 3) Fer, 4) Lucas1 and 5) Taco. I don't get how Taco could accept this. He should've just left.
Since this didn't work and Coldzera got tired of all the issues with the hierarchy (he was the star player) he decided to bench himself and in a fashior where Zews had to stand-in instead of a real player.
This actually solver their issues. 1) FalleN, 2) Fer, 3) Lucas1, 4) Taco, 5) Zews. Entry Taco, mid-man Fer, Lurker Lucas1, Support Zews and FalleN played AWP and shared responsibilities with Fer. Fer's number rised, Taco had higher impact rating, Lucas1 didn't have any issue with either calling nor role nor hierarchy and Zews might have been the worst player to ever play t1 CSGO in a team as good as this, but it worked out for them.
So with this revelation the most suitable option would be to find the best player for the Zews role. But instead they went to kNgV, a guy that would step on the toes of FalleN, Fer AND Lucas1, all at the same time, while having an ego so big that he would expect to be top 3 in the hierarchy.
When this didn't work they just cut Lucas1 and added Meyern. This was a risky move, but I think it is the correct one to make. He is young, can climb like Fer, Coldzera and Taco did under Dead, Zews and FalleN, he can be a roleplayer that can step up whenever he wants.
So the next logical thing to do would be to kick kNgV and see what they are missing. Fer can either play lurker or mid-man, FalleN will go back to full time AWPing and be mid-man or 2nd entry, Taco or Meyern can be entry or support. So just find a guy similar to Meyern and you'll be fine. The perfect player would be Luken, but he recently signed for Sharks. Perhaps some ex-luminosity/ex-INTZ player as a placeholder until they can find someone that fits the bill. No need in rushing this roster move.
When they finally have a healthy roster and team dynamics, I am certain FalleN's job as a strat maker will become easier.