I can’t include Helm in the snap without having the same problems explained here, which caused the Helm snap to switch to classic confinement: Classic confinement for existing Helm snap
Also I don’t think in this case it would be a good user experience even if it could work due to the way these Kubernetes tools share configuration in .kube/config for example.
With classic confinement I can install kubectl, helm and helmfile separately and use the release channel I want for each tool e.g. kubectl 1.15, helm 2.16 branch. This is often desirable.