Hull's tenure as UK City of Culture failed to fully engage with Black, Asian and Minority Ethnic (BAME) groups and adults under 35, a report found.
The 2017 programme of events "did not link enough" with the city's ethnic population and neglected the Kurdish community, the University of Hull said.
But it praised the boost in tourism and growth in the economy the events brought.
Former boss Martin Green said: "No project can reach everybody."
In its report, the university's Culture, Place and Policy Institute (CPPI), said: "Engaging with the 16-34 audience segment proved to be unexpectedly hard.
"Future cities of culture should develop specific plans for this demographic group. This plan would recognise significant differences within the 16-34 demographic, and would seek to strengthen connections with schools and universities."
The CPPI said it was "essential to identify how culture is defined by different audiences" and noted how "audience representation was notably higher among those in their 50s and 60s".
"The internationalism of the city's 2016-2026 cultural strategy was not fully reflected in the UKCoC programme," the report stated.
"There is clearly scope for a greater focus in future cultural programming on the international connections of the city, including those of Hull's diasporic communities."
It also added the tenure was "more successful in... focusing on disability arts and on LGBT issues".
However, researchers praised a spike in overnight trips and boost in tourism revenue from £178.1m in 2017 to £180m in 2018, 800 new jobs created since 2013, as well as new private and public investment.
Mr Green, who was the chief executive of Hull UK City of Culture, said the city should not be viewed as "metropolitan".
"Hull is diverse in one way but not in other ways," he said.
"There are areas that we need to continue to investigate."
Coventry has been chosen to be the UK's City of Culture for 2021.