Carlos Sainz is just a few points off Gasly despite driving what we know is an inferior car to Red Bull. To be honest I'm not sure why Red Bull moved Sainz over to Renault and then cut him loose, he's been developing nicely and has always been a good solid points-scorer. At McLaren he looks even more mature and is getting very good results.
I think the Red Bull driver programme has always been about finding star drivers, not finding good drivers.
If you look at former Toro Rosso drivers, very few of them were hopeless. But equally most of them weren't Schumacher or Vettel 'good'. Which is why a Buemi for example got his marching papers.
Sainz is good but IMO was clearly a step below Verstappen. Even now, he is only slightly ahead of rookie Norris when he should be spanking him. Sure, Sainz is generally a solid driver and in this case would have done a better job in the second Red Bull but Marko is looking for a next Vettel, not another #2 driver.
The irony is that if Sainz had been patient and accepted another year at Toro Rosso, he would have been in the Red Bull this year....