AWS' new T3 instance type is set to run with T2/T3 Unlimited enabled.
The way that the current EC2 plugin is designed, we cannot create T3 slaves which have Unlimited disabled. The EC2 plugin has a checkbox to enable/disable. However, it uses the default if this is unchecked.
The EC2 plugin should probably take that setting exactly and use it to set the value. Thus, to use T3 instances with bursting, the Jenkins admin must manually check the box.
Alternatively, you could have a drop-down with options like: 1. Enabled 2. Disabled 3. Instance-type default