I think you are mixing a bunch of points and arriving somewhere altogether different.
"Peaking", itself, is an interesting notion. Ideally, with proper squad rotation, a team will be at "peak" at all times. Thats the point of a squad.
Fergie tended to build momentum through the season. Not unlike Poch really. And he did it year after year. Mourinho brought a level of competition Fergie hadnt had in a while, and so he rose to meet the challenge. I dont know how much "peaking" had to do with any of it. Fitness is but one aspect of the game. Id argue that the competition sharpened Fergies (and Utds) mentality. They had to step up, and so they did.
I think mentality is the biggest thing in managing a top team. All other things are generally equal, or near enough, its mentality that separates the winners from the losers.
Mourinho builds a siege mentality, an intense environment, and as a result he burns teams out. He thinks its a winning thing, really its just unsustainable pressure.
Fergie was a real winner. Just hear his players talk on the TV now, Ferdinand isnt he most articulate but you can hear in his words just how important winning is. That was Fergies thing, not "we have to beat them" or "we must not lose to them" or "Everyone is against us" - it was "we need to be the best" "We need to be the winners". It was as though the opposition was incidental.
Everything then falls under this. Conditioning, training, tactics, ethics... all if it is lead by mentality.
Which is why I contest the importance you are placing on "peaking". Arsenal, like every team, are driven by their mentality - not suddenly turning into energiser bunnies thanks to some conditioning algorithm.
And when you look at Arsenal, their mentality - from the top down - the "narrative" that they play their best football when their season is over stands scrutiny.
As soon as their season, perception being the key, appears to have got away from them - the pressure lifts, they play, and get results, and suddenly they are bearing down on what they thought they lost. Which is a nice wave to ride, its easy to be motivated then.
And I think you just keep saying 'no, it's nothing to do with conditioning / peaking, it's mentality', but aren't offering any reason as to why it can't be the other way. It stands scrutiny as much that it could be mentality as it does conditioning.
I can't find the quote (I guess it may have been in Fergie's book) but he has spoken before about how Mourinho made him realise he needed to start seasons faster. Obviously he's a winner. Obviously his players see him as a winner. But if he's such a winner, why was he not 'trying' to start seasons as well as he could? What was holding him back from doing that? I'd argue that he needed to tweak their conditioning so they were able to start fast, and maybe they suffer a little bit more mid-season, but at least then Chelsea haven't pulled away. Saying 'they had to step up' does not easily conflate with Fergie being a serial winner who accepted nothing less. There must have been more to it than that. Why did Fergie accept less in those early games, if it is all about mentality?
Mourinho builds a siege mentality but I am talking within a season. He always starts quickly, he did it this season and he did it last season. That is not to do with his siege mentality overall, that is how he starts seasons, as he always does. And why is that? Is he more demanding with his team talks?
Arsenal don't just turn into energiser bunnies, and frankly I used to be totally bought into the idea that Arsenal played better when the pressure was off until I learned more. And I saw what Poch was doing with us, which then made a lot of sense. Arsenal playing well with no pressure is as much a narrative that we are only able to put the pressure on rather than be the leaders. I don't buy it - if we had more quality and depth, we'd be able to get out in front. And relative to our pre-season expectations, we were absolutely way ahead of where we needed to be last season for example.
I don't think they turn into bunnies, but I think there is a noticeable difference in the tempo that teams adopt over a season. Sometimes Arsenal are ponderous, and sometimes that's because they are just bad. But a lot of the time, I think they play a higher tempo because that is the time that they have prepped to play it, and that gives them a greater chance of winning, as that does to us. But let's say they played a high tempo but couldn't sustain it over a game, because they were knackered and hadn't peaked...they'd be more likely to get picked off and not win those games, because their strategy isn't aligned to their condition. That's why I think form is predictable. Mentality is different a part of it, but I don't think everything comes underneath it. I think it is all linked. How you motivate our group depends on the players we have, and how you get them to play, and train, and condition them is all linked to what kind of players we have. It is hollistic.
I compare our games against Swansea, WBA or Bournemouth at home to our games against Everton and Man United recently and it is absolute night and day, in terms of the tempo we adopt. It is a completely different pass selection that we use, we are a lot less safe, a lot more aggressive, and we are pouring forward at every opportunity. We are more patient in some of those earlier season games, and sometimes this gets written off that we just couldn't get going, but I think it's somewhat deliberate. We play a more patient style in earlier games or when we haven't peaked, and when we play a more aggressive style, it's because we are peaking, and we know we can sustain it rather than getting picked off. And maybe now, because we're peaking, we may be able to sustain it twice in a week for example, but we absolutely couldn't do it earlier in the season. We played a high tempo vs Madrid and then a slow game against Palace where we just needed the result. But there's a big argument to say if we tried to play the same way against Palace, they could well have picked us off particularly later in the game.