#4 - Luvdisk
Luvdisk is what I like to call a useless pokemon. It's stats are generally bad, and it's only really worth catching for heart scales. It is likely the worst pure water type out there, next to the Magikarps out there. Luckily for you, you can teach it flail at level 40! That'll make a lot of difference at that point, when many well-raised pokemon could one-shot it.
#3 - Feebas
Now, I have to say, I personally like Feebas, but it's basically the second Magikarp. They're almost impossible to find without incredible patience, and they're even harder to evolve. I'd probably hate them more, except I actually found one of the squares they're found in, and managed to evolve one. They're easy as anything to catch when you find them. (I have about 7 total, 3 migrated into Diamond). Still, beforehand, it's completely useless.
#2 - Seedot Family
Seedot is a bit of an annoyance to me, being that it can only learn a (possibly) offensive skill is at 1 level before it evolves. Even after that, it's very difficult to use without teaching it anything from a TM. It's only guaranteed damage skill before level 30 can only be used on the turn it is sent out, unless you constantly switch it out and in. Overall, it's not really worthwhile.
#1 - Wurmple
Ah, Wurmple, essentially the Caterpie/Weedle combination of R/S/E. This is the main pokemon that makes it most apparent that the 3rd generation wanted to be the first. What's most fun about it, however, is the fact that it's evolution cycle is completely random, meaning that you aren't guaranteed one form or the other, and most of the time, the evolutions aren't worth much in general themselves. Wurmples are just bad.

Horrible Mentions:
Plusle/Minun: Useless out of a team. Not even any really good skills either way.
Illumise/Volbeat: See above. They're essentially the same.
Keckleon: Bad stats. The unique ability doesn't make up for the fact that it has no worthwhile skills.

Volbeat and Illumise

Im still not sure exactly what the point of them is.
they arent even that good, seperate or together

WHY, YOU'RE RIGHT.
I added a Horrible Mentions section, which I planned on making for Plusle/Minun and Keckleon. Wow, those 2 are so insignificant, I completely forgot about them

I always thought Shedinja was pretty overrated because of its ability. At least most other Pokemon stand a bit of a chance if something super-effective hits them.

I'd say
5. Seedot
4. Wurmple
3. Illumise/Volbeat
2. Cas/Silcoon
1. Skitty

Okay, I would disagree with your assesment of Kecleon. It's got no point if you include it on your team, sure, but it's an invaluable tool for checking Hidden Power types, which, given that Hidden Power is a replenishable TM in RSE, is very useful indeed.

Keckleon is not bad, in my opinion. You have to choose your moves wisely, though.

at the very least, kecleon is a somewhat annoying customer in the battle frontier - it usually uses trick, and is strong enough to survive at least one hit so you can end up with a choice band...

Could it be that Pokemon like that were designed for Pokemon Contests, and not for battling?