Well, I don't wan't to start a "war" between whos best or not, everyone has their different play styles but I'l explain my journey.
I finished shade impulse and the distant glorys with OK, he was "ok" and he was my favourite.
But after I opened up and played other people who have more flexible and unpredictable play styles such as Golbez and Kuja, I realised he holds no place for me. (all though I love running around as a Sage btw

)
basically I'm going to find a flaw in his play style. Lets start.
Speed- No doubt he is the fastest person in the game, safe Tidus in his Ex Mode, but, you don't need to run that much unless you plan to fight on the ground, and since most battles end up in the air, theres no point. Personally I put everyone with Omni Air Dash but I only walk/run to toy with the enemy just for fun (I have fun on maximum every time BTW its easy after a while). And hes attacks come out very quick to, lets do a mini description:
GA= Ground Attack
AA= Air Attack
Ground:
GA-GA2-Sword Shower- This is a good move I guess, Hits a couple times good for Iai builds. 7/10
Blizzard-Blizzaga-Quake- will like always miss, even if you block, counter sometimes. 2/10
Air:
AA- AA2- Guiding Sweap- I prefer the ground version IMO same thing I guess. 6/10
Thunder-Thundaga-Flare- I like this one, great homnig and it acts as a sheild, great ability. 9/10
Evasivness- What Evasivness? Everyone except Tidus dodges the same, so yeah, that changes in Duodecim though since Tifa can spin around her enemies during an attack.
Predictability- When I want to test my combo's I usually go to people in this order : Tidus, Cloud then OK, come on, he only has 4 attacks if you think about it, and if you vsed me youd be long dead since I tear close rangers apart with my Arrows.
lets recount.
+ He's Fast
+ All moves branch
- Speed is only essencial in abilities
- Very Limited skillset
- Only 1 decent ground move
- Certain combo's arent guaranteed