For a balanced team IMO they need:
- a striker like Cavani, MM, Belotti, Suarez etc. who will run and work all the time. Neymar, Di Maria, Mbappe and Icardi is too much attacking, too little defensive contribution
- a midfielder like Vidal, Partey, Kante etc
- a starting left back and right back. Bernat before injury and Florenzi are decent backups, but nowhere near good enough both ways for a true CL contender
- a starting CB
And now it's rumored Mbappe told them he's gone next summer, Neymar is injured a lot, Verratti too. He could be successful there, but it's just too many question marks and ifs and buts