Are You kidding !
It took 4 year for Ash to get 1 win out of Paul ! Furthermore, He manage to win due to Infernape Blaze . Before that he lose every single battle against Paul.
Don't fool me ! You didn't watched DP at all .
Conventional storytelling generally dictates that the protagonist doesn't beat the antagonist until the very end of the story, hence why Satoshi didn't defeat Shinji until their climactic Sinnoh League battle. One of the reasons Satoshi's victory against Shinji is such a good moment for
Diamond & Pearl (and the anime franchise as a whole) is precisely because it had been held off for so long. Satoshi defeating Shinji earlier would have negated a lot of the impact of that battle in general.
Anybody who really did Watch DP would be furious at you might now.
Paul used Tactic more then any other trainer did in this entire series .Ash Was the only Normal Trainer who mange to get 1 win out of him with Infernape sheer Power. Cynthia is the E4 champion & Breaden is frontier Brain with 3 legendary.
Can you imagine A Series where Ash only lose E4 member , Champion and Trainers with Legendary Pokemon ?
Well , Thats how it was for Paul.
The problem with this is that Shinji was not the main character of
Diamond & Pearl. He was an antagonist who only showed up occasionally and needed to be built up as a strong trainer so that Satoshi's eventual victory over him would feel like it was worth it. Shinji, much as I enjoyed him, would not have worked as a main character. His purpose was to be the obstacle Satoshi would overcome in the future. Satoshi's purpose was to grow strong enough with his Pokémon in order to defeat him.
And a
Pocket Monsters show where Satoshi and Pikachu could only lose to champions and E4 members would likely be a very boring one. There needs to be some element of drama present in things like Gym and rival battles.
Paul still bested Ash during Sinnoh League. It was Infernape Blaze that beat Paul , Not Ash's tactic. Paul even see though Ash's plan to get Electirvire come close for Pikachu to beat him with Iron Tail.
Without even getting into the fact that Shinji also relied on his Pokémon's special abilities and wanted to harness that very same Blaze for himself, I think you've missed the entire point of what Goukazaru and Blaze meant to the rivalry with Satoshi and Shinji. So let's quickly recap:
The main theme of the Satoshi-Shinji rivalry centers around whether or not the bond between a trainer and any of their Pokémon can make them stronger. Satoshi telling Shinji this is what causes Shinji to challenge him to a battle in the first place and what essentially kicks off the rivalry, and Satoshi's philosophy - reminiscent of Reiji's - is why Shinji doesn't like him at the start of DP. It also forms the basis of the two's differing training styles, Shinji working only with Pokémon he deems strong and maintaining a certain distance with them while Satoshi takes an active part in his Pokémon's growth and development. Shinji's Hikozaru struggles under Shinji's training style, so he eventually deems it worthless and releases it, after which point it becomes Satoshi's Pokémon.
Hikozaru's Blaze becomes a plot point when it triggers during yet another Satoshi-Shinji battle and causes the Pokémon to go out of control. Satoshi calms it down with a promise that the two of them will become stronger "together" (he brings this up again when Moukazaru goes out of control later). Throughout the rest of
Diamond & Pearl this is precisely what happens. The two grow: Satoshi into a stronger trainer, Hikozaru into a stronger Pokémon that eventually evolves twice into Moukazaru and Goukazaru. And it's only as Goukazaru does it finally control its Blaze ability. This is all only possible because of Satoshi's training style, a point Reiji makes when Hikozaru evolves into Moukazaru. So when Goukazaru's Blaze activates during the battle with Shinji - and it should be noted that Reiji
explicitly states that this was what Satoshi was gunning for - it's a vindication of everything Satoshi has argued with Shinji about. Shinji comes to respect Satoshi and his beliefs on Pokémon training because he was on hand to witness Hikozaru becoming stronger.
Shinji didn't beat Satoshi in the Sinnoh League in any sense, and he wasn't better than Satoshi on that day. He came in with a pre-conceived strategy, had that strategy effectively countered, and all six of his Pokémon were knocked out. That Goukazaru even came to a place where Blaze could become a realistic factor was down to Satoshi's training style. As far as that particular battle goes Satoshi and his Pokémon were better, if only by a very tiny margin.
