I agree that you should never discount athletic qualities with recruiting, but Kounde is extremely athletic - speed, explosiveness and jumping abilities are all athletic benchmarks. You cannot teach someone to have more fast-twitch muscle fibres than others, and Kounde is a very explosive athlete. Remember for a moment that Tim Cahill, at the same height, made an absolute mockery of much more aerially-dominant defenders at set-pieces because of his athletic ability. Being tall doesn't automatically make you aerially dominant (David Luiz, anyone?), specifically at set-pieces where you actually have to challenge players with force in the air.
That said, he's more or less the same prototype as Christensen/Rudiger at CB (except probably a bit better on the ball) and Reece James at RWB/RCB (except a little better in the air). I don't understand what he offers to the squad beyond being an excellent rotation option in a 3-atb system, and a potential waste in a 4-atb system. Given than Tuchel is historically the tinkeriest of tinkermen, it makes no sense to lock us into a single formation.