Here's a study published by the NHTSA in 1999 regarding stopping distance with ABS versus without. From the paper:But that is just speculation. Is there any proof to what you observed? Any studies, research? It is a known fact that ABS increases braking distances compared to what an expert can achieve. Using ABS compared to slamming on the brakes and skidding? I don't know.
For most maneuvers, on most surfaces, ABS-assisted stops yielded distances shorter than those made with the ABS disabled. The one exception was on loose gravel where stopping distances increased by an average of 27.2 percent overall. Additionally, the vehicular stability observed during testing was almost always superior with ABS.
Keep in mind, the last comprehensive study was 25 years ago, prior to the addition of stability control and traction control being standard. That's 25 years of improvement in the mechanics and computers, so the one spot where stopping distance with ABS was further than without has likely improved.
(If you want an idea of the testing methodology, the NHTSA utilized a test driver with 17 years of professional test driving experience, had the driver do six runs with each of nine cars in nine scenarios empty and loaded to the max weight rating, and performed ABS runs without any manual brake pumping at all.)