Set picklist Value as default value in a field on sales a engagement Runtime Object

Question

I managed to customize the standardValueSet of the CompletionDisposition field on ActionCadencetracker runtime object, but I failed to assign values as a default value using metadata xml:

<fullName>My Value</fullName>
      <default>true</default>
 <label>Completed Cadence</label>

I deployed the updated fields values metadata back using Workbench successfully, but on the UI, the field's value is not being set as default.

If the above is not doable, can we have the completionDisposition field as required so the Rep must select a disposition value before removing the target? Any help is highly appreciated!