I was thinking about Series S, dropping as low as 576p in one game that offered 120fps

The scenes were more action orientated and the drops were very temporary. Its not especially odd. I don't think they contact devs everytime they see fps drops, Its not like Dirt where one console literally has last generation LOD on the vehicles. Or DMC where you had crazy differences in performance at times (50+ fps difference) and a completely unlocked fps that was running all over the place.

As far as the 120fps mode. Both systems miss their target a fair bit and thats what they expected, but 10 frames lost at 120fps is not the same experience as 10frames lost at 60fps. Given that they did not even expect 120fps this generation, I think its fair to say they will not be as harsh on 120fps targets as they are on 60. None the less they highlight PS5's advantage here, but neither are especially stable unless you have VRR. What likely confuses them is why the Xbox Series X version runs better in RT mode but worse in 120fps mode. There is nothing on paper or that they're aware of that would cause this difference. Maybe in time they will get a better grasp on the topic but right now their guess is as good as yours. If you have an idea, @ one of them on twitter.

But they have been contacting the devs on the comparisons in portions that favor PS5. They forgot to mention that the drops on PS5 in CoD were bugs... that is why they are getting their credibility questioned. For one side they are giving excuses, minimizing the issue or calling the devs to confirm, for the other it is "well it is less powerful so nothing unexpected". That is the reason why I say they are struggling to cope with the games showing different then what they expected.

Did we get any rumor of PS5 tools being late or Xbox tools arriving to cover this comparison?

Again, are they contacting devs for a few drops during setpieces or bigger wide set problem? 

I think you're misunderstanding the purpose of DFs videos. They never spend much time looking at mean fps because it would make for pretty short clips, instead they analysis performance overall and focus in on any stress points. Stress points can be a very small % of gameplay so they won't make a huge impact on a mean fps, but that doesn't mean they're not noticable in a play through. i.e everytime a boss performs a certain attack. This has been typically of every video they make, if there are stress points they focus on it, even if its just a cutscene. 

Both games have a very stable FPS, they mention this, you also see it in the frame graph. But at 60fps the PS5 version shows occassional high percentage drops (going from 60fps to 50 or less), they stated this doesn't occur during gunplay when facing actual enemies. They don't mention mean fps because they're more interested in places where people will actually see drops and places where the system exhibit differences. None the less they do state and show that both systems are the majority of the time 60fps.

Anyone who watches DF's content should able to be aware of the fact that its just a tech breakdown. They look for technical aspects to speak about, I find it super interesting but at the same time when they zoom in to grass blades to show the difference in resolution between 2 versions of a game or show a few frames dropping in  the heaviest action, I know full well that won't impact my experience at all. If anyone comes away from a video like this thinking the PS5 version is bad or feeling defensive of it, they're watching more with their feelings than with their brain. And this goes for a lot of their content. People need to stop getting touchy about things they literally wouldn't be aware off if it wasn't for these tech breakdowns.