I think it’s because Cynthia was constantly portrayed as this monster with a Garchomp based on how much they shilled it and that’s why it seems like it’s a more amazing feat for Lucario.
In all honesty, if things were realistic and the right moveset (even then) Pikachu should have been the one to defeat Garchomp if not Infernape.
there's a big discrepancy in cynthia's hype(especially from sinnoh) and what cynthia actually does. Vs Iris she basically cheats to win and against Ash, with the exception of taking out pikachu via drag along, it seems she's mostly succeeding off ash letting his pokemon getting tagged a bunch.
sinnoh garchomp was this supreme unbeatable pokemon for a supreme unbeatable trainer. Journeys garchomp is a chump who
-> needs to cheat to beat haxorus
-> is dealt heavy damage from just one move by one of ash's weaker mons
-> isn't even chosen for amplification vs ash suggesting he's basically interchangeable with cynthia's other mons as an ace
They’ve been doing this weird thing where they quickly get Pikachu out the way to have the ace of Ash’s current team not lose after Pikachu so they can finish the match and it’s worse because Pikachu actually knows Cynthia and this isn’t a random opponent. Lucario had no connection with Garchomp besides random egg magic they made up .
I mean i'll take it because cynthia taking out pikachu with drag-along is like the only moment where she actually feels like an impressive trainer/strategist.
It's also decent holistic hype for Pikachu. Could be seen as Cynthia's basically saying "damn pikachu's too good, gotta take him out to beat ash". Pikachu actually looks a lot better than garchomp right now which is ctazy to imagine considering wherr we were at in sinnoh.
The actual masters tournament has treated pikachu a lot more favorably than i expected with pikachu repeatedly being called ash's best and pikachu basically operating as a team buster vs flint and cynthia.
Was expecting it to be more like lucario as ash's greninja and Pikachu as the warm up act
Will say pikachu having a "connection" with garchomp is a stretch. I'm not sure they've ever even interacted with each other.