Just looked at ArcMap; it does appear that Symbology and Labels default to the alias name. Not aware of any setting to change it the field name when using the Symbology/Labels tab. However, the Definition Query tab (and Query Builder) default to the field name. I know you didn't ask about it, but you can change the Attribute Table to display the field name rather than the default alias. Open the attribute table > click on the drop-down on the left > and uncheck the option for Show Field Aliases. Really the only way I am aware of to set ArcMap so you always see the field name would be to change the aliases so they equal the field name; not sure if you have the privileges to do so if you are working with an enterprise GDB.
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