Almost all of the English Invasion bands started out as cover bands. That includes the Beatles and the Rolling Stones. A lot of those bands, however, were very talented, and quickly moved on to writing material for themselves. The Manfred's singer, Paul Jones, wrote this one.
I'm starting to think that bands that got the best advice were the ones who moved up into the "making money zone." The Beatles had Brian Epstein and George Martin playing big roles. The Stones had Andrew Oldham, whom I am beginning to think was smarter than he's gotten credit for.
Maybe it's just a tough business. Certainly the Kinks, the Who, and the Hollies had talent to spare. All three of them had as much entertainment value as the two big winners. They also had good writers. So, weak management? Poor planning? I don't know enough of the details to sort that out.
Bad advice was definitely involved in some dramatic crash-and-burns. Paul Jones decided to go solo, and so did Wayne Fontana ("Game of Love," with the Mindbenders). Both of them were leaving bands consisting of very talented musicians and some reason to expect further success. Who advised them on that move? Both singers went off the radar immediately, and the only subsequent material that I've heard was very weak. Both bands went on to greater success than they'd had with their original singers.
Want to have some fun? Get ahold of the WF and the Mindbender's Game of Love LP. It's hugely entertaining, and musically excellent. Those fellows could really play.