Evolved versions of baby not counted as evolutions

There are no wild babies and these pokémon have standard catch rates (of course, Pikachu and Clefairy are below average, but so are starters). The point is to reward the extra difficulty in catching evolved mon so it's understandable that these still only give 100 dust.

You might have a point but babies cannot be encountered in the wild so maybe that's why

You get no bonus for those pokemon because while they are evolved forms of baby pokemon, they are STILL considered basic pokemon. So they get the same catch reward as other basic pokemon.

I've recently noticed when catching pokemon like Clefairy, Pikachu, and Jigglypuff you only get one candy per catch.

Are you sure you are only getting one candy? A normal catch gives you three candies. No one else seems to have noticed you said "one.".