I've watched football since 1998 UCL Final and 1998 FIFA World Cup. Zidane was more decisive in the big games and better than Ronaldinho. Zidane was better than Iniesta and Xavi too.
Villa went for 2.1 M. The add-ons were available only if he spend two more seasons in Atletico. He went to MLS after one season. So 2.1 M of euro for Villa.
I would sell ter Stegen and sign Donnarumma. Donnarumma is already better IMO and he will improve. Stegen since Liverpool game is very average, time to cash in.