How do you want to measure it? I mean, I guess you would just check Gamepass numbers from the CoD release month and compare it with the month before but that would be illogical.

Many don't just subscribe for a single game. They subscribe because they know they will get constant releases of games like that. And there will be people who have subscribed already months ago because they knew games like CoD will release. There will be people subscribing in a year knowing there will be X different CoD games and most important, a part of every new subscriber will pay for years.

I don't pay for Gamepass because there is Halo or Forza or whatever on it. I pay for it because there are Halo and Forza on it (and the other games obviously)

And not to forget, more players means more people paying for in-game currency and stuff like that. That's the whole reason why Fortnite prints so much money. CoD had more players than ever which probably means it also has more people paying for skins or the next DLC. 

Your right, its not as easy as looking at Gamepass subs 3 months down the line, and comparing to how they were 3 months before.
However, if the jump in subscriptions was big enough, you could do that calculation (compared to what you expect they lost in sales).

Ultimate its only Xbox themselves that will know. 
Maybe there is more micro transactions on Xbox side, and that then makes up for some of it, that could happen.

Even if we got revenue numbers from Call of Duty, its hard to compare one years vs another.
Its a tough question to answer.

I guess time will tell, if it was a good choice, by how they handle it for the next call of duty?
Like if there are more gamepass changes based around CoD? or if next year its not in gamepass?

The majority of PS4 players could have upgraded and bought a PS5.

I think its safe to say though, as long as Call of Duty is available to purchase/download on PlayStation, GamePass won't be siphoning off any of Sony's player base.

I would be more worried about the collapse on pc than on Xbox. Also Playstation barely growed, what ever growth PS5 had was lost with PS4. This was with MW3 being received poorly and BO6 fairly well. Especially since PC is growing pretty quickly where PSbox sales are stagnating.

One thing this shows is that dropping the last-gen consoles is overdue. I'll be shocked if the 2025 COD releases on them with sales having gotten this low.

Only 30% up over MW3 isn't great considering (IIRC) that game underperformed by COD standards, being basically a $70 expansion pack.

Gamepass continues to have a corrosive effect on game sales, further evidenced by how much game sales have cratered on Xbox in general.

30% up is for PS5 sales. Across all platforms it's down 15%.

I know, I was referring to PS5 sales, probably should have been more specific.

At this point, Activision could ship a blank disc in a box that said "Call of Duty" and it would still sell like 20 million units, but this year's performance isn't impressive by series standards, at least to me.

Xbox committed for the next 10 years to also put COD everywhere (PlayStation and Nintendo).
That means the Switch 2... which is rumored to be around PS4 levels.
So potentially the next few COD, atleast might still have PS4 support (though it could be dropped)

Every Playstation sale and every PC sale is an Xbox sale. Soon every Switch 2 CoD sale will also be an Xbox sale. Xbox is not taking any losses with gamepass. They weren't getting profit from Playstation/PC/Soon Nintendo from Call of Duty sales pre-acquisition.