I mean, Piper Halliwell is for all intents and purposes her most remembered role (and yes, I know that Holly was later on Pretty Little Liars). Granted, when Charmed first started, Holly Marie Combs was definitely the least known of the three leads. People already knew Shannen Doherty from 90210 and Alyssa Milano from Who's the Boss? (and to a lesser extent, Melrose Place). Prior to Charmed, Holly was on a show called Picket Fences, which really wasn't that popular.

You forgot the low budget and horrible B movie known as Dr. Giggles she was in before Charmed.

I've recently heard the argument that Holly Marie Combs was never really a good actress to begin with. The last four seasons of Charmed (basically, the Paige seasons with Rose McGowan) were mainly her "angry nag" style of bitter acting.