Ok, so the canonical argument is the best one I've heard against it yet. I can appreciate this. I'm a big fan of the games but I didn't read the books or anything. What about covenant & other alien weaponry? Does chief auto sinc with those too?
I believe the scopes of Covenant and other Alien Weaponry are all digitized and as such, he uses his armour to gain access to their optical feeds and just display what the weapons show by default on their feeds, which is Ammo/Energy, Heat, The Reticle and other designs. Text and whatnot is then translated through the Suits systems.
So yeah, his armour just auto syncs and streams the current weapons information once the data-transfer contacts in his gloves hold onto the data-transfer contacts in the weapons hilt/riffle holding point. The UNSC is just lucky that the Covenant use a similar system to feed information to Covenant Soldiers (Mostly, the Sangheili).
Another fun thing is that for weapons which don't have data-transfer contacts on them, The suits HUD essentially emulates and predicts where the gun should be pointing. For Regular Soldiers, those
Eye Pieces they wear over one eye is where the weapons hud gets displayed. They could also theoretically use it to scope, but since its only one eye, they would have to close the other and/or have to use the scope anyways because they aren't capable of just absorbing the recoil like a Spartan can... Normal marines would mostly use
Shooting Glasses for the task of weapon stuff though.
But yeah, the entire HUD and armour Systems in Halo can get pretty indeph, so changing stuff around and retconing for no reason does get annoying
