There's a bit more to it. The reason vaccines weren't developed previously for other coronaviruses is because in trials for a RSV vaccine, 80% of treated kids that got infected needed hospitalisation and two died, while something like 5% of the control infections needed hospitalisation. Due to antibody-dependent enhancement.

So yes there are immunopathology concerns with eliciting a T-cell response, and inducing a humoral immune response has the potential to make things worse.