Hi Vincent,
Greetings from Syncfusion support.
We have validated your query and found that currently there is no option show the tooltip always in RangeSlider. So, we have considered your request as a feature and the status can be tracked from the feedback portal link.
Note: We will prioritize the features every release based on the demands and priority. So, this feature will be available in any of our releases. If you have any more specification/suggestions to the feature request, you can add it as a comment in the portal.
Regards,
Praveen G.