The philosophy of voice acting for cartoons has completely reversed itself.
Can you tell whose voices these are by just listening to them?
Can you tell whose these are by the sound alone? Can you even understand what they are saying?
we can use that
To me (and of course I'm wrong) a good cartoon voice actor has to have 2 main attributes:
1) An obvious unique and pleasant vocal sound.
The greats like Daws Butler, Don Messick, Mel Blanc and more all have a naturally unique distinct sound-even when they are not doing a cartoon voice.
It's like having a quality instrument as opposed to a rusty old out of tune one.
This is why many oldtime cartoon voices came from radio, where the quality of the voice is so important.
Movie stars are known more for their faces than their voices (especially today) and when you replace their faces with a cartoon character's face, you lose the movie star's value, because the audience can't tell who is doing the voice - and don't care. They just want to believe in the characters themselves.
2) Specialized acting ability.
Clear Diction: You have to be able to clearly understand what the actor is saying (unless he is purposely mumbling for some story or character reason)
For example, listen to Ranger Smith's line at the top. Esp. the second half "Maybe I can do something.. before the commissioner..."
Try to read that line yourself as fast as Don Messick does and still make it all sound so clear and perfectly inflected. It's not easy. Don was a real pro.
A wide range of inflection - and the ability to control it and tailor it to the meaning of the dialogue and character.
If you read everything in a flat monotone, you aren't adding anything to the character.
Vocal acting is even more important in cartoons than in live action, because cartoon visual acting is not as easily controlled as a live actor's visual acting.
A colorful unique and rich voice adds a lot of personality to an animated character, whether you have a huge or tiny budget. It's instant personality.
That coupled with a good design gets you half way there.
Bill and Joe may have made super cheap cartoons, but they had the good sense to use really unique and appealing character designs and combine them with distinct and super qualified voice talent. At least in the beginning.