Rodri being out weakens their set piece defending and that they cannot replace that within the squad unless putting Stones in the Rodri role. But we all know Stones isn't durable enough to play week in week out.
Could put Gundogan there but then Citeh lose the box crashing element of Gundogan game.
Not to mention KDB is an offensive threat but he's not box to box. Rodri is the key to their entire transition as well. KDB/Foden/Bernardo doesn't get the ball in dangerous positions without Rodri. Kovacic is NOT as progressive as Rodri nor does he get away with the same skullduggery.
I don't see how people can say arguably the best holding mid in the world for at least 3 years is "not a big loss".