The "strategy" in FFX

[Karifean]

That's why I liked the Omega Ruins: You actually had to devise strategies to go through enemy encounters while making sure that you capture the enemies and that you take as little damage as possible (the more rare enemies barely spawn around the save sphere). Things like figuring out Master Tonberries are very vulnerable to sleep or that using Sentinel against Halmas was very worth the turn just felt rewarding. Well, except for the fact that the entire area was smurfed up because of random forced-ambush encounters with Great Malboros...
Once you get past the correct-character-to-win-parts - which I think happens around Mt. Gagazet - the entire game just feels much more challenging and rewarding.

Also, Rikku is one of the most versatile characters in the game. Stealing is the only convenient way to obtain items for the Use ability and those can deal more damage than Auron - not to mention when you mix two together. Aside from that, she has a healing item that heals the entire party and greatly outclasses Pray, she can instantly kill any machina enemy and she can also cast Shell, Protect and Haste.

[Nebulance]

I think it was a good idea to make each character have a speciality which made you use them in combat. Except that Kimahri and Rikku are effectively useless unless you send them down another person's path. Yuna, too, lacks a dedicated enemy to fight, but at least she has Aeons to make up for that. But I mean, look at it:

Tidus - Fast, nimble
Wakka - Aerial
Lulu - Elemental, magical
Auron - Armoured

None of the other enemy types have strengths that Kimahri, Yuna or Rikku are designed for. Sure, I typically send Kimahri to bro out with Auron and Rikku plays with Tidus, but neither of them does it as well as the dedicated. It's almost not worth the effort. Abusing the game to make Rikku and Tidus super quick is the only way Rikku even becomes useful.

I agree with this. Kimahri continually ends up as the worst character in my games -- largely due to his position on the Sphere Grid, and also because he gets captured at what I consider to be a crucial point in the game -- right before the second battle with Seymour on the bridge in Bevelle. That's the point where I really start leveling up to handle him properly, and Kimahri ends up missing out. Recently, I've forced the issue of just leaving him in all battles and he's finally useful. I still go to Auron/Tidus in the so-called 'big battles' however when I need someone that can pierce armor.

Until recently, I've never really given much attention to Rikku but I've become more interested in obtaining all the items I need to design weapons and armor that I want to make me invincible to Marlboros and whatever else. Due to that, she's seen a lot more time and is actually quite formidable now.

I think with Kimahri and Rikku one really needs to pay more attention to giving them time to develop, as it seems a lot more natural and easy to do so with all the other characters due to their intrinsic strengths against certain characters, as you've mentioned.

[Jessweeee♪]

Kimahri is as much a Red Mage as he is a Blue Mage I think. A jack of all trades, a master of none

Rikku is...different. If you steal from enemies often she'll gain experience as well as anyone else while simultaneously making Use a lot more useful. Her high speed makes her and Tidus a great team for those boss fights where you manipulate the CTB system so it never gets a turn.

[Jinx]

Rikku was always one of my best characters. I usually have Rikku, Tidus, and Auron. Tidus and Auron do between 12-15k damage, and Rikku does about 10k damage.

I don't care what people think, Wakka is a troutty character.