The outputs from the utility based model would be the same as from the model it was derived from - a bunch of actuator/motor outputs. The difference would be the utility-maximizing action "under the hood".

Utility based models are most useful when applying general theorems - or comparing across architectures. For example when comparing the utility function of a human with that of a machine intelligence - or considering the "robustness" of the utility function to environmental perturbations.

If you don't need a general-purpose model, then sure - use a specific one, if it suits your purposes.

Please don't "bash" utility-based models, though. They are great! Bashers simply don't appreciate their virtues. There are a lot of utility bashers out there. They make a lot of noise - and AFAICS, it is all pointless and vacuous hot air.

My hypothesis is that they think that their brain being a mechanism-like expected utility maximiser somehow diminishes their awe and majesty. It's the same thing that makes people believe in souls - just one step removed.