Keep in mind Ash's Hawlucha is very fast, so it's "Body Slam" actually gains enough force to badly damage stuff, even with its low weight. Also, Hawlucha will not self KO itself, you can compare it to the wrestler Rey Mysterio which, although seemingly frail and weak, is actually very durable, strong and has high flying capabilities.
Noivern is a better Pokemon than Hawlucha??? I'm sorry but on what basis are you making this claim? Also, Boomburst is not Noivern's signature move. Chatot, Exploud, Swellow and Flygon also learn it and 3 of them get STAB on it.
Unfortunately for you , It doesn't matter how fast Hawlucha is !
It need to attack from very high to reach enough speed and produce enough force to do real damage.
But By the time its reach that high and laugh its attack , its would enough time for a Pokemon to move away and point its paw toward Hawlucha.
Kind of like How A mare ''Pound'' from Frokie was enough to KO Hawlucha.
Plus When Hawlucha use ''Flying Press'' , Its body become defenseless ! Giving a perfect opportunity to foe to attack .
Also , Anime=/=Game !
In the game , A pikachu can beat a Kyogre But that doesn't mean Pikachus are really strong enough Kyogre in Anime .
I'd rather have Ash get Doublade or Aegislash if he gets a Ghost-type. Trevenant would not suit him imo, and would really, really scare kids (especially girls) if it shows up every episode. Yes, Trevenant is a tree, but it is a haunted tree.
Oh please , If that were true then Gengar would be Banned from Pokemon Anime!
However , Kids aren't weak enough to scare of Ghost Pokemon like Gengar or Trevenant.
Also , Ash catch's a grass type in every region So I rather prefer Trevenant then a Boring Assed Skkido.
Truth is , Its fun to see soft side of a scary pokemon.
and trevenant is a dead kid lost in the woods... Not exactly child friendly if a main character...
Ya and , Banette is the Angry sprit of a Doll that was abandon by Kids ! Even though Banette has a per-evolution.
Dude , Its just a Legend !
If Banette is an Angry spirit of Abandoned Dolls then it wouldn't have a Per-evolution since its directly born from a Doll .
Same Way , Trevenany isn't a spirit of a Dead Kid!
Its Just a Friendly pokemon that protect the Forrest from Evil People ! Which mean its Heroic Pokemon that Ash deserve .