It depends on the speed they are going. On a gradient of 6-8% the help with drafting can still be significant. If the climb is steeper 12%+ it's true, the effect of drafting is minimal. There are tiny differences between the best riders in the world and every minimal help you can get at this level is important. I've read recently a scientific article about drafting and they found out that even if the riders are going as slow as 13kph, there is still some effect of drafting.
On the really steep gradients having a teammate with you also helps when you get in difficulty. Not so much because of the drafting (like we said, it's minimal), but mainly because you have a visual point of reference, a teammate who is pacing you and the only thing you concentrate on, is following the teammate. It may save you 5 seconds. It doesn't sound much, but in the end those 5 seconds might be important.
In the scenario the OP suggested, if Pogi remains alone with multiple Ineos and Jumbo riders, it becomes especially handy if those riders are also high in the GC standings. If let's say Tao and Kuss attack and get clear and they are both less than a minute behind Pogi in GC, then Pogi has to chase them, the other Ineos and Jumbo riders just follow. In the Tour you rarely see those really steep slopes like you find in the Vuelta or Giro, so on the majority of climbs the drafting is still important. With every extra effort Pogi has to do in comparison to his main rivals, the accumulative fatigue increases and in the end that can be crucial.
In your example of Col de la Loze, if I remember correctly Lopez and Kuss attacked first, then when they were 10s ahead Roglič jumped from Pogačar and caught Kuss who was in the meantime dropped by Lopez (or he eased up waiting for Roglič). Kuss was then pacing Rogla for about a minute. Loze is very steep at the top (average around 10% in the last 4km), but is very irregular. There were also some flattish sections and I'm sure Kuss was of some help for Rogla. Again, not much, maybe 5 seconds, but sometimes that's all you need. We all know it wasn't enough in the end, though. He needed much more than that.