I've never come across any direct quotes from producer Jack Wrather on the subject; Wrather acquired the rights to the series in 1954.
It seems as if Wrather chose to upgrade the production to give it a "second wind": he immediately rehired Clayton Moore to play the Lone Ranger, added location shooting (outdoor scenes), and for what proved to be the final season, Wrather invested his own money to film in color.
Around that time, forward-looking TV producers invested in color production upon the valid theory that color TV would soon become widespread and an industry standard. They also shrewdly realized that a color production would command a higher price, and have a longer shelf life for syndication-- another wave of the future.
Also, Wrather may have gambled on using a costlier but visually richer format because it made the show more attractive to movie producers. Indeed, after that final season was filmed in color, Wrather decided to withdraw from further negotiations with the networks and instead shopped "The Lone Ranger" as a feature film-- two LR movies were released.
FWIW, when I watched this series as a little kid, I was OK with Chuck Courtney as Dan Reid. But even then, he stuck out like a sore thumb.
Nowadays, watching the show on retro TV channels as a old guy (61), I find his dorky character much more annoying. I can't really say why, but even his Sears & Roebuck cowboy outfit seems distractingly corny. It looks like Dan Reid wandered over from the set of "The Roy Rogers Show".
I don't know the back story behind Dan/Courtney's character, e.g. if they thought the show needed a new face to appeal to kids or something like that. I seem to recall that he first appeared on an episode without Jay Silverheels/Tonto, so I wondered if they came up with Dan as a substitute if Silverheels wasn't available now and then.
Courtney was in his mid-20s, but he looked like a teenager. Maybe they thought he'd appeal to teens, which became a big selling point in the 1950s entertainment industry.
I also find his relationship with the LR, such as it is, awkward and unnatural. I suppose they could claim that Dan doesn't openly call the LR "Uncle" because it would give away their relationship and provide a clue to the LR's true identity. (Especially because one usually addresses an uncle by name, e.g. "Uncle Joe", at least among family.)
But that's a stretch-- in fact, the whole secret identity/mask business is pretty shaky. They pretty much trapped themselves during the "origin story", when the LR's mask and secret identity were deemed necessary to avoid pursuit by arch-enemy Butch Cavendish. But Cavendish was soon captured, so they had the LR claim that the mask/secret identity was vital to his vigilante mission of preserving law and order in the West.
I read somewhere that Fran Striker, the principal writer on the LR radio show, hated being stuck with the mask; he accurately complained that it required the LR to constantly explain or defend it to every stranger he met.
OK, I'm rambling again. I veered off on all that just to mention that another weakness of Dan's character is that he's just thrown into the mix. Where did he come from? What does he do when he's not being the LR's substitute sidekick? 'Tis a puzzlement!