You're right, it takes much longer to pick "no" or "customise" because the way it is implemented in 99% of the tracking tools is that it has to be opt-out and to do the opt-out the site loads a pixel that places a special opt-out cookie. Not saying this is a good thing, but it is a reality that it takes time to load so many opt-out pixels.
So there is a big change that this is a lot of outrage while there is no dark pattern here.
Except I guarantee if choosing the "allow all cookies" option took 50 seconds that the very first thing that product would prioritize is getting that down to sub-second.
Granted, it could still be some sort of a polling situation vs. just a deliberate fake "make this take a really long time", but it still doesn't matter - it's still a dark pattern because the site owner is deliberately OK with the "opt out" solution being so onerous that hardly anyone would wait that long.
So there is a big change that this is a lot of outrage while there is no dark pattern here.