The AmetysXSLTHelper from the CMS extends the one from the runtime.
The AmetysXSLTHelper from the WEB is standalone.

The AmetysXSLTHelper from the WEB should extends the one from the CMS (beware of possible conflict between some static methods, some method might need to be renamed or rethinked)
Or, the three helpers could be independant and renamed (and maybe more specialized)