feature.getContent() method returning 'codes' for the fields with Coded domain values instead of 'name' for features from related table.
Below is the sample in which when you select any feature on map it will show its related records details in side panel.
If you observe in the side panel value for the field "SHORT_TEXT_DOMAIN" is "NO" which is the code.
Where as in the case of feature layer it is working fine, it seems to be an problem only with related records.
It is observed that if we update the _layer property of the feature(related records) with new instance of feature layer object ( new featurelayer created from related table URL) then we can see the expected behavior. to see the expected behavior please uncomment the line no. 114 and 115.