Again, one that is more a question of extent than the point, but that is a bit of an embelishment.
After the 17-18 season, when he was first tried at LB to get us to the end of the season, Zinchenko has played more games at LB than any other of our LBs in each of the following 3 seasons, up until the last season when Cancelo had a worldy on both sides of the pitch.
In 2 of those seasons he played as many and/or more games than the next 2 put together.
He is no doubt a squad player, I use that term myself, he shares that role with with others and is often not first choice. But he also often is, and has been more than just a back-up, for at least 3 of his 4 seasons as a LB.