DB was scheduled to be animated regardless of its initial popularity because of the explosive success of Dr. Slump (this is why there's only about a year's gap between the late-1984 first chapter of DB and the early-1986 first episode of the anime; OP and Naruto by comparison took 2-3 years to...
I think the instability of Kaio-ken makes going that high impractical, and even if he could stack, say, 10x or higher onto SSJ, SSJ3 would still drain less power and strain the body less
That demon realm shit was CC's idea. I came up with Freeza using Ki altering drugs to achieve God Ki after spending time training in a Rosat dimension.
That doesn't exist outside of fanart, but if considering LBSSJ4 to be the equivalent to Blue Evolution, the multiplier for 5 would then be over 20 times regular SSJ4. But LBSSJ4 pretty much is SSJ5 anyway.
They cheapened it straight after Freeza surpassed SSJG Goku from training for 4 months and not even obtaining a god form. Guys like Jiren and Cell Max, Beast Gohan etc. just cheapened it further.
It looks like Vegetto still uses Kaio-ken instead of Evolution Blue in Heroes. He just beat the main body of Ozotto (Gohan absorbed) in his Blue Kaio-ken state.