They did indeed, for €15 million last summer. Kabak was very much ahead of Todibo at Schalke, though perhaps that wasn't a surprise given he was already their player and Todibo was on loan (albeit with an option to buy for a high fee). Former Man City defender Nastasic is their other first choice CB. Todibo only really seemed to play for Schalke when they adopted a back 3, or when coming on as a sub. Also worth noting that in that Barca vs Inter game he was also in a back 3. He's not really tested in a 2 CB formation at a high level and as per my post earlier in this thread I think he'd need time and a very good, experienced, all-round CB next to him to do well there.