the two biggest examples of this for me (cuz honestly a lot of bands either totally suck from the beginning to me or stay really good till the end)
koRn: fucking good band until the 2000 era and then they just dragged out the same old thing for ten years..
Marilyn Manson: Daisy Berkowitz was that band like Tony Iommi was black sabbath.. zim zum was pretty good replacement, but he didn't write the material. after they brough in John 5 that shit went in a sucky direction.