Put it this way, if Gabriel had a White like defender on his side and Saliba has someone like Zinchenco at RB a lot of people would be saying it's proof that Arteta was right and that Saliba isn't ready for thus level and should still be out on loan.
The job covering all the space that Zinchenko leaves behind is a mammoth task. Especially when as a defence we have a substitute CB who isn't quick enough to cover for Gabriel when he has to shift over to the other side to cover for Zinchenko.
Gabriel is one of the best defenders in the league, there's hardly anyone I'd swap him for playing for our rivals. We're lucky we have both him and Saliba.