It can be the best for certain situations, but not all. No bait is going to be “best” in all conditions. I’m actually not a big spinnerbait fisherman myself. The only time I use them consistently is when the water is muddy. A Chartreuse spinnerbait with Colorado blades is absolutely killer in muddy conditions. They give off a ton of vibration, which drives the fish crazy.
You can use spinnerbaits throughout a lot of the year and do fairly well in most cases, but there’s going to be baits that will be much more productive for these situations.
For Smallmouths, I never use spinnerbaits. They will hit inline spinners pretty well at times, but I prefer using plastics for them. I’ve caught a lot of Smallmouths on tube jigs.