The point here isn't who he should have fought, but who he shouldn't have fought. I thought that was obvious in what I said.
These fighters were somewhat competitive because they were very experienced fighters. Simply put, they knew how to fight. Joe Louis was a GREAT fighter!!!! Louis fought a number of talented fighters and crushed them!!! Unfortunately, a sportswriter tabbed Louis' title defenses as the "Bum on the month" fights. This misnomer took on a life of its own and people think that Louis fought a bunch of handpicked chumps, when in reality, Louis fought a number of tough fighters that were talented and capable.
There probably is no problem fighting second-tier challengers if all the first-tier challengers get a shot. At least one of these "bums", Buddy Baer, I would judge way above the average contender from any era, with a solid won-lost record for his time, and a huge knockout record. He was also physically imposing. Baer would be a worthy opponent for any champion from any era.
Personally, my interpretation of this series of fights is that Louis wasn't really slipping or past his prime, but was a little lackadaisical and uninspired for these fights because he was fighting a very busy schedule and taking on opponents who weren't viewed as threats or big fights. The Lou Nova, second Buddy Baer, and second Simon fights(which came after this string) are all vintage Louis, in my opinion.
For sure he shouldn't have fought Harry Thomas, Jack Roper, Johnny Paycheck, Al McCoy, Guz Dorazio, Tony Musto, and Johnny Davis. These were worthless "contenders." They should have been allowed nowhere near the title. They are there to pad Louis' highlight reel. Tony Galento and Red Burman are extremely dicey challengers. Burman wasn't very good (don't get distrscted by the padded record) and Galento was a bum. He only makes it to the second list because he nearly had Louis out of there. Others not listed, while, decent, would likely not have been challengers in an era where there were tight standards. Godoy had several recent losses coming into the fight. Abe Simon was clearly limited. The Billy Conn fight was a novelty. The challenged weighed in under the light heavyweight limit!