Now that Gladbach is in a collective meltdown I wouldn't necessarily vouch for Ginter's every single performance, but I'd say in general he's quite reliable.
CBs/GKs aren't like other positions anyway: if you do well it's nothing more than expected, but if you make a mistake it's a catastrophe, hence the value of players like Ginter, who are solid all around players and usually don't feck up. Tah for example might have more talent than Ginter and might turn out to be the better player eventually, but how many points will his mistakes and inconsistency have cost Leverkusen by then? And for how long would they get to use him on that level, before he'd want to make the next step. I mean look at Leverkusen's results this season: for all the talent their young players may or may not have at the back the team often seem like they couldn't hold on to a lead if their life depended on it. They have dropped five leads already this year, that's about as much as they usually tally over an entire season. If everyone else wasn't in crisis mode all season, that could easily cost them top four.