I will pretend that you didn't just compare this shit to One Piece.
STOP
1.) I know this is subjective, but I don’t think this manga sucks. If I did I wouldn’t have chosen to translate it in the first place. I’ve honestly read worse than this.
2.) No I’m not, in some ways it’s more like Fullmetal Alchemist. I’m only saying your argument is the reverse of what One Piece fans on Reddit have complained about Luffy not struggling or losing enough to main villains, for multiple arcs. I’m not making this up.
You’re complaining about Isaza, an average teenager (NOT your average teenage shounen manga protag), who’s still a novice at combat, and using his stone powers, losing to a guy who clearly has more skill and experience at both. What did you expect to happen? This fight lets us know Isaza could potentially get as skilled as him. The kid has to start somewhere.
As for Enami’s Army, they’re clearly not used to fighting wars, nor is their military might as strong as the other Kingdoms. Hence why they’ve continually suffered losses and betrayals. The Watatsumi Family already understood this, which is why they were initially hesitant to go to war with Hiiragi and Takadono.