Lately I've been wondering about why Wukong is subject to mana use when other champions, and especially similar champions in abilities (Garen) or playstyle aren't. Upsides to Mana having I can think of: Manamune (but you really shouldn't have one on Wukong). That one Defensive Master ability. Downsides: Running out. Wukong Specific: Giving away Decoy. (see below)
Let's compare Garen and Wukong: (Ults omitted due to myriad other threads on them)
Q: Garen: Speedboost and Silence, 90 bonus damage + 1.4 per AD. So actually full damage + 0.4 extra + 90 extra. 8s cooldown.
Wukong: 150 bonus Damage. Flat. Armor debuff. 5s cooldown.
All in all Wukong has less cooldown and 60 more damage for not having +0.4 per AD. So once you exceed about 150 AD, Garen's does more damage, but has longer cooldown. Arguably way better due to speedboost and superiority of silence though.
W: Garen: A passive that will be flat out better than Wukong's innate passive 10 minutes into the game, be always active independent of enemies (Hello Dragon/Blue/Red!) and gives more boost. An active that absorbs a flat amount of damage. Can't avoid CC. Lasts 3 seconds. 18s Cooldown.
Wukong: Decoy. Grants stealth, does minor AE that can pop Banshee's Veil. Scales with AP unlike everything else Wukong has. 10s Cooldown. Makes your mana bar go down visibly to the enemy, making it painfully obvious you used Decoy. Also fails if any sort of buff/debuff/DoT animation is on you because it won't be on the Decoy. Can avoid CC. (if they fall for it)
Unless someone like Veigar decides to ult your Decoy because he is completely oblivious to the fact you used it, Garen is almost guaranteed to absorb more damage. Only advantage is being untargettable, especially to avoid CC, or pop cooldowns on CC. (Because Garen could just tank the damage to pop cooldowns on damage abilities anyway). Useful to get away or initiate for Wukong. Useful in every situation ever for Garen.
E: Garen: The Spin. Damage. Break slows. Don't be slowed as hard. Scales with crit, supporting a wider build. 105 damage + 0.7 AD per half-second, for 6 hits in 3 second duration. 9s cooldown.
Wukong: Triple-Split Dash. 240 + 0.8 AD damage to up to three targets (non-designated). Attack speed buff. 8s Cooldown.
This is a hard comparison. Both skills are good, and not at all similar. Garen's is arguably better though due to its slow-breaking and lowering nature, and the overall way higher damage output as soon as enemies stay in it for 1.5 seconds, although Wukong has the advantage of it being a gap-closing Dash. (though Garen gets gap-closing from his Q obviously, while this is Wukong's gap closer). Cooldowns virtually the same.
Now, apart from the listed differences, and advantages (often in Garen's favor), the main difference of course is that all of those abilities for Wukong use Mana, while Garen is entirely cooldown based. Not only do you run the risk of going OOM (though yes, this is rare if you don't spam like mad, but still possible), it also disadvantages Wukong because it gives away the fact you used Decoy.
While you could argue that taking away his mana use would give him better sustain and that's not the intention, there are other manaless champions of similar damage/squishyness levels already.
Basically what I'm looking for in this thread isn't "Lol yes Wukong so UP needs a buff." But rather arguments for why Wukong shouldn't have mana, and especially arguments for WHY Wukong should have mana. If after thorough deliberation we cannot think of any reason why he should (and honestly, maybe I'm just overlooking something here and I'd be glad if someone could point out a reason), then that's a statement we can make toward Riot.