I'll give Lilly credit, she's actually having G show some weakness, albeit in what sounds like an unfair move rather than an actual disparity in skill, power, or tactical blind-spot. All depends on how it's framed. "I can't believe that evil pokemon did that in a battle that was so unfair" or "You lowered your guard, it was inevitable".
There's also the possibility of "he just got lucky" which I'm usually OK with as
elements in a fight because unpredictable elements are part and parcel in any real fight and what separates pros from amateurs is ones ability to deal with that unpredictability. But if it's the deciding element for an entire
arc I have to wonder what the intention is. If it's the core of an arc the situations surrounding the outcome of the fight has to serve some sort of narrative purpose, right?
Although a more important question, why am I putting more thought into this than Lilly?
Injury Arc- This is new, and a good one to boot! I mean, really?...A punch to the Heart? I know I shouldn't be surprised given Lily's penchant for middle-school level story writing, but still. I'm not even going to go into the logistics as to why the heart is one of the hardest organs to damage with a "sucker-punch" because it would involve a lengthy explanation of why people just never go for the upper torso when in a fight (quick explanation: it's easy to protect and has a strong rib-cage also protecting it). This is just another one of the long list of examples of Lily completely abandoning practicality and logic in favor of drama and edge. Oh, and of course I'm doubting it's the actual move "Sucker Punch" (which is a very strong move when used wisely and could mess a Gardevoir up) and is literally just a straight up actual sucker punch because Lily thinks Gardevoirs are invincible killing machines for some reason.
The red horn on the Gardevoirs chest is a physical manifestation of it's heart. Unlike humans Gardevoirs don't have a rib-cage protecting it, it's just out in the open. If it is a straight boxing match and the heart is a vulnerable location it would make sense to go for it were the opportunity to present itself. People still go for the chin and liver, and those are smaller spots relative to the size of the person compared to the big red horn relative to the size of a Gardevoir. Real life boxers in the ring go for the head so much because it's a force multiplier. Even thought the head is more difficult to hit consistently, a hit to the head generally counts more than a hit to the torso. Old timey boxers went for the torso over the head because they didn't wear gloves and hitting the skull un-gloved full force your liable to break your hand. Also why those boxers hold their guard so low. Torso hits were the bread and butter of any given boxing match so the guard is put in-front of the torso. If the heart is a force multiplier akin to the head it would make sense to go for it even if it were to be guarded. If it is a force multiplier akin to the chin or liver, it makes even more sense.
As for "easy to guard", a basic bitch Peek-a-Boo Guard can be broken with a well practiced uppercut and could be used to strike the "heart". Nobody does that in real life because a guard breaker like that can be used to strike the head which is a much higher value target. Things get more complicated the higher one's skill and the more reliable parries and dodges are as means of defense, how susceptible the defender is to feints, and I'm sure adding bullshit pokemon powers and physiology to the mix changes this even more. I don't expect any of that to come into play in a interesting way since Peet doesn't strike me as someone who really considers or cares about any of that. I don't read the comic for tactically interesting fights, I read it for hilarious ineptitude. Once again I'm putting more thought into this than Lilly.
Showing my extremely limited Pokemon knowledge, I had no idea Sucker Punch was a specific move in the game.