As porpoising is influenced by many things, i think its more likely that its a combination of things, not only the suspension as the "magic-solution". I also think that Mercedes would have been able to solve it already, if it would be about the suspension "only".
But anyway if you read this Newey interview closely, there are three very interesting parts that shows some of the areas why, in my opinion, Ferrari and Red Bull are the fastest cars and why Mercedes has a lot of problems:
The first thing is that he says the new cars tend to be more front-tyre limited than the "old" ones. In 1998 with the introduction of the grooved tyres, it was pretty much the same. McLaren and Ferrari used different concepts and back in that area it had a lot to do with lowering the CoG, front stiffness and weight distribution. Ferrari in particular pushed as much weight as possible to the front and put more downforce to the front and also added stiffness to the front, but anyway - having experienced a regulation change with similar implications, Neweys experience certainly helped a lot, as did Byrnes experience at Ferrari.
The second one is that he said there is more than one airflow under the car and making them work together is important. Of course this surely is no secret, but having experience how to achieve the best way of how to do this to extract the best performance, is probably another reason why Red Bull and Ferrari gained a performance advantage from Neweys and Byrnes experience. Newey suggests, that Ferrari, as Red Bull, have considered purpoising during the design of the car, but intentionally decided to accept a higher amplitude of porpoising and that being just a different approach to his one: "I guess they feel thats the fastest way around, so you trade a bit of driver comfort and initial braking performance.". By replying to the question if he had thought going into that direction as an experiment with "your set-up is driven by your aero-map, so what works on one car won't work on another", i think he clearly says that he believes that Ferrari, too, has considered porpoising in the design-phase already but just handled it in a different way. As Ferrari is not loosing lap-time, this sounds very reasonable, and again Neweys and Byrnes experience probably helped both teams a lot. Experience with ground effect cars helps a lot and that it makes a difference, is proven also by McLaren. Their rapid recovery is not a conicidence. With Neil Oatley they have one of four engineers left in F1 who already designed ground effect cars in the early 80's. Mercedes does not have a single engineer with experience in that regard.
I do not want to put sucess down to one person as F1 is about a team- but with a big regulation change like that, the experience of people like Newey and Byrne cannot be rated high enough and is a huge advantage.
The third interesting detail, i think, is that Newey says he may will "trying to get in a new position where i can be involved as an overview - which i think is what Rory Byrne does at Ferrari now." Clearly describing Byrnes contribution on the F1-75 and that he directed the way to go and the concept of the car. But thats only interesting in terms of contributions of certain individuals. One may be interested in that, one may be not.
Anyway - i think that Newey and Byrnes experience, next to their genius, not only with ground effect cars, but with with front-tyre limited regulations, is a major reason why Ferrari and Red Bull are much faster than any other team. And why they will probably keep their advantage for 2022. Mercedes lack someone like Newey or Byrne. They have great engineers without a doubt, but no experienced ones in relation to ground effect cars and regulation changes like that. Thats why they basically stayed with their "old" concept of "micro-sidepods" and going extreme with this concept, instead of a new one. Also the dominant team, history proves that, tends to take less risk in that regard. If you look closely, the five teams with experienced engineers in that regard have improved - Red Bull, Ferrari, Alfa, Haas(because of Ferrari) and McLaren, while the teams without experienced engineer did not improve - Mercedes, Aston Martin, Williams. Not very technical at the end, just some thoughts, but i think sometimes there also should be some things like that in such a forum.
But anyway - thanks for sharing the link to this interview. Interesting read.