Ndombele and SMS are very different players though, SMS is attacking powerhouse first and foremost, Tan guy is much better defensively. I think with Emre and Bentancur we are more or less covered in CDM/DM department.
IMO non of them get close to ndombeles energetic gameplay. The guy has it all. Energy, pass, dribble, carries the ball forward. Eye for assist.
Emre is okaish, average in everything, just gets the job done.
Betancurt still needs more developing.
In an ideal world, we Would get the 2 of them, ndombele and sms.... As both are what we need.