What are the shortcomings of Azure ARM Templates ?

check this article. It may be useful.

https://blogs.sentryone.com/melissacoates/getting-started-with-automated-arm-deployments-in-azure/

Limitations and Rules for ARM Templates

A few final things to be aware of when getting started with ARM templates:

Certain resources are not Resource Manager-enabled (most are enabled).
Certain resources can’t yet be exported from the automation script in the Azure Portal (you’ll see a message the top if this is the case).
Certain regions are not supported for certain resources.
There are API versions which are supported for each resource.
Unique names (across all of Azure) are required for certain services (and rules for requiring lower case if it is a URI).