Because in her mind there is the spiritual origin of Mewtwo, as long as she can develop power from the spiritual origin, it can drastically boost Gardevoir's spiritual power, and the enhancement of spiritual power equates to a comprehensive boost in Gardevoir's strength!
Usually, the focus of training is on physical fitness and move speed, while the rest relies on the spiritual origin for enhancement. In terms of over-leveled battle capabilities, Gardevoir might not match Charizard, as her only skill to fight over-leveled battles is Mewtwo's exclusive skill, Psystrike.
Using it once will drain all of Gardevoir's power, making it a skill where failure means death, with a very low tolerance for mistakes.
However, in terms of level upgrading, Gardevoir is much stronger than Charizard. Although both are now at the same level, Gardevoir reached Gym level seven days ago, while Charizard reached it only two days ago, and the gap between them is gradually widening.
The most important reason is... Mewtwo intervened to help Gardevoir develop her spiritual origin. Since it originally belonged to Mewtwo, guiding it out was incredibly simple, requiring no repeated MEGA Evolutions from Gardevoir to stimulate it.
The power guided out by Mewtwo is more straightforward, direct, and pure, making it faster to absorb.
Neither Ash, Gardevoir, nor Mewtwo ever thought this day would come when Mewtwo would assist the 'enemy' who took its spiritual origin, actively helping the other absorb his power—it's like seeing a ghost.
Compared to Gardevoir, who has a shortcut, Charizard can only push himself harder to unleash the power of the Rainbow Wing within him. He, too, has a shortcut!
However, this shortcut isn't aided by the shortcut provider (Ho-Oh). Relying solely on his and Ash's strength, drawing power from the "stubborn mule" of the Rainbow Wing is exceedingly difficult.
Charizard thought of a method, but Ash firmly rejected it, which was—beating him half to death to force the Nirvana Power inside the Rainbow Wing to be triggered.
Ash would never watch his Pokemon be beaten half to death, let alone do it himself. That's absolutely impossible!
Using this method to enhance oneself is akin to competing with Gardevoir out of spite.
Charizard isn't afraid of hardship, but that kind of enhancement method is beyond just tough—it's pure self-torture! Hence, Ash would never agree to it.
Charizard had to reluctantly abandon the idea of using such a method for enhancement, opting for a steady, step-by-step approach. Unless he finds Ho-Oh one day to guide out the Rainbow Wing's power, he'll have to wait for a last-ditch battle to unleash its power.
Apart from these two competitors, Pikachu, the team leader, has reached Gym Peak.
Ash finally understands why Pikachu's rebirth is considered an S-level lottery. Originally, due to rebirth, Pikachu's level was already lower than Charizard and Gardevoir, but now, it's surpassed them!
Although his aptitude in six-dimensional abilities far exceeds that of the average Pikachu, there's still some gap compared to Gardevoir and Charizard, theoretically making his level growth unlikely to surpass those two Pokemon.
Yet Pikachu inexplicably exceeded them at rocket speed. Now at Gym Peak, when fully unleashed, facing Elite Level battles is no problem. Adding two buffs, he could absolutely clash with Champion Level!
This is Pikachu-sensei, the eternal ace.
The advancement of the three powerhouses is gratifying, and the other Pokemon's progress isn't slow either. Ash gives special training to all his Pokemon equally, even giving extra training to some, like Blastoise.
Compared to Charizard and Venusaur, Blastoise's rate of improvement is very slow, and his battle power is far inferior to theirs. Unlike other Pokemon, the relationship among these three is unique.
The identity of Kanto's Three Starter is ingrained in everyone's mind, subconsciously affecting the Pokemon.
Blastoise is naturally aware of the Starter family title, and with Charizard and Venusaur joining the team almost at the same time—within ten days of each other—
In these circumstances, their power shouldn't have diverged greatly. Yet now Charizard and Venusaur have left Blastoise far behind; no matter how hard he tries, catching up seems impossible.
Blastoise even fell into a period of depression, but Ash's special training helped him to stand back up.
Blastoise's MEGA Evolution grants him a new Ability, Mega Launcher, which increases the power of all wave-based skills by fifty percent.
It might seem like just a powerful enhancement skill, but Ash noticed a key point.
Wave, also known as Aura, is Ash's familiar domain. In terms of Aura, few in the world surpass him. Blastoise has the potential to learn Aura, and after mastering Aura Power, Ash could use his own strength to aid Blastoise's growth.
For Blastoise, having support to enhance Water Type power would be ideal, but if not an option, prioritizing strength enhancement is the path.
Compared to Charizard and Gardevoir, Blastoise's disadvantage is enhancing not Water Type power but Aura Power. Although integrating Aura with skills can significantly enhance skills' power, like Water Pulse, where if the wave is strengthened, the overall power of Water Pulse increases, raising the confusion chance.
However, the problem is that for Blastoise, learning Aura Power is like starting from scratch, making this path extremely difficult and unsuitable for the current Blastoise.
Nevertheless, compared to Charizard and Gardevoir, Blastoise's advantage lies in having Divine Domain Level personal guidance, with unreserved power adjustments, enhancements, and fusions.
For them, only divine materials aid in enhancement. Although Mewtwo assists Gardevoir, it can only help develop her spiritual origin. Ash, however, can directly synchronize with the Pokemon, providing Blastoise with far greater assistance than Mewtwo offers Gardevoir.
With Ash's special training, Blastoise's level, while only at Professional Peak, has made tremendous progress. Without Ash's interference, a MEGA Evolved Blastoise can go toe-to-toe with Charizard who doesn't use Sacred Fire.
Charizard six.
Ahem, after all, it's still Professional Peak versus Gym Level. Even leveraging MEGA Evolution into Gym Level, with some attribute restraint, battling a Pokemon like Charizard, capable of surpassing levels, remains quite challenging.
Without Ash's tricky Aura Power teachings, Blastoise's chances wouldn't even reach forty percent, barely two.
The last of the Kanto's Three Starter, Venusaur, has also reached Mid-Gym Level, like Charizard and Blastoise, where level doesn't represent actual power. Fully unleashed, without relying on Ash's Aura Fusion, Venusaur can still contend with Elite Level!
Blastoise still finds it challenging to catch up to the other two, but at least with Ash's help, there's some hope now. Without it, Blastoise could only watch the gap widen until it's no longer visible.
Now, with Ash's support, Blastoise can barely keep pace with Charizard and Venusaur. Once Ash finds a suitable Divine Domain Item for Blastoise, that's when he completely catches up with the two!