How to convince my boss we need to define relations

We are using TypeORM and mySQL, boss is ux and frontend, he doesnt want relations because they didnt use them in their previous company.
this decision led to horrible typing, we have to cast all types when we want to manipulate data from an entity.
long and complicated queries when we want to get data from other tables.
I am jr frontend, and had to do some backend lately and it is a mess, should i try to convince him or just keep writing bad code?