Make it more than 9 years.
Our midfielders this year (Pjanic, Bentancur, Rabiot, Ramsey, Matuidi, Khedira, Can) scored only 10 goals in 52 matches and assisted 18 goals.
This is worse than anything we had since the return from serie B.
In Conte's 3 years, the worst our midfield did was: 25 goals and 23 assists in Conte's first season.
In Allegri's 5 years, the worst was last year, pretty much with this year's midfield: 15 goals and 14 assists
Del Neri's midfield had: 16 goals+20 assists; Zaccheroni's and Ferrara's had 16 goals+16 assists; Ranieri's worse was: 12 goals+27 assists
Our worst midfield stats wise, since coming from serie B, was the one from the last two seasons. Last year the midfield made 29 goals+assists, this year 28 g+a. The previous worst after 2007 was 32 G+A in 2009/10 when we finished 7th in serie A.
Before serie B, assists weren't counted so I can't make a comparison, but if we count only goals, the last time a midfield scored 10 goals or less was in 1994/95 when our midfield (Conte, Deschamps, Marrochi, Sousa, Tacchinardi, Fusi) also scored 10 goals. In this particular season, though, we had Baggio to connect midfield with attack (Ravanelli, Vialli, Del Piero) and if I count him among the midfielders, then I'll have to go further back to find such an impotent midfield as the one from 2019/20.