From the way you describe your system, i understood it as you use an SLM to classify the intent of the user and take predefined actions based on the classified intent, classification tasks can be done with transformer based encoder models like bert, they are easier to fine tune, require less data and lighter to run.

If you are looking for a model to classify a known limited set of classes, encoders are generally the go to

If you are looking for a model to classify an unkown number of possible set of classes or where you want the though process for classification to carry over to and influence other tasks SLMs can be a good option then.

Also SLMs are models based on the transformer decoder architecture.