Use Ideate Explorer for Revit to eradicate non-standard Text and Dimension Styles.
Ideate Explorer can show us all of the Text actually being used in the project. We can use Explorer to merge these styles. First we'll select all these extra 3/6" Arial Styles and then put them into our Properties selection. ...and then use Properties to swap those instances for the correct style. When your return to Explorer you'll see that those non-standard styles no longer exist and can now be purged. This same process can and should be applied to your Dimensions.