I couldn't have got the shots handheld without flash. Shooting closeup without flash requires a tripod.
I have great difficulty doing as well with my Graphics and Cambo. These have to be shot from tripod and are much slower working than a Nikon. They're absolutely impossible with small unconstrained fish in aquaria and with live insects that won't hold a pose for very long, are very difficult with flowers and such. What usually ruins my flower shots is wind, which can move the plane of best focus between the time I focus and compose and the time I get the shot off. Yes, I still use flash.
I agree,using a flash is the easiestway to get plentyof lightand a fast shutter speedbut getting the exposure right can be tricky;best to use a flashmeterand avoid the inverse square law,which fails when you get really close to the light source