Surveys published via Survey123 Web do not retain the default value field. The surveys are neither prepopulated with the default value, nor is the default value used when submitting the survey. The data tab shows that blank entries are recorded. I have only tested with number fields (specifically integers which are not required fields).
In fact, when creating a survey in Web, the default values don't seem to be saved at all. When I re-open a survey to edit it further, the default values are lost.