TL;DR: The grapplehook can stay in the game, but the grapplehook should be designed around the combat and not the combat around the grapplehook.
Even if you do not take the fights with the grapplehook at all, you can clearly see, that the combat is heavily designed about using the grapplehook. This design decision makes the combat way easier than in previous Halo Games.
E.G. There are more enemies in combats than in previous Halo games, but they shoot way slower. You can see that very good on legendary when you fight against jackles. Jackles on legendary used to have Plasma Pistol Gatling Guns with an ultimate fast fire mode, while in Infinite the shooting speed stays very low.
More enemies with less shooting speed make it way easier to flee with or to fire back with the grappling hook. Faster shooting speed on higher difficulties would lead to more deaths, because the one enemy you flee from is way stronger.
More enemies with slower shooting speed allow to grapple away, because the one enemy shooting at you is significantly slower and the other (additional) enemy is out of position.
Slower shooting enemies allow to snipe everything one by one pretty easy compared to earlier Halo games.
Additionally the AI is pretty dumb at most of the time not aggressive as it could/should be. I do not want to write a poem about this, but here some examples:
Enemies do not aggressively move forward to you, enemies flank you only 20% of the time (I often stand at 3 way pathes and only in few cases one enemy comes down one path, most of the time only high ranked enemies),
they keep standing in front of your vehicle and want to die (if elites jump, they stay in my lane), even on legendary enemies get angry when you melee them instead of punching back,
enemies do not seek cover as good and effective as in previous Halo games, elites role in random directions (looks cool and makes them less bulky then broots, but is completely useless) etc.
All these AI problems lead to the point, that even in situations where you normally would have messed up, you can grapple away or grapple a core and feel like an (undeserved) badass.
The whole tactial and strategical aspects of the combat like in Halo CE are missing. That is one more important reason, why (for me) Halo CE is way less repetitive than Halo Infinite.
P.S. Big battles and structures wouldnt be a problem with the grapplehook, if you design it rightâŚ