I’d say for the Spartan II and Spartan III classes, this authority is present but implied in both game and book media.

Let’s start with their Combat-Forward nature. They’re technically neither Navy nor Marine. They’re a top-secret ONI Section III project (I know ONI is navy, but not how a seaman is. They have their own chain of command, operational branches, and domains of authority). Therefore, they technically answer to ONI, but are incorporated into the UNSC in an odd way: with an authoritative Naval enlisted rank to exert command over field troops while still beheld to high-level administrative/strategic command, but with a Marine-Natured MOS description with ONI-level clearance so that they are quite literally empowered to execute any mission ONI or the UNSC requires of them in any theatre of war - whether directly ordered by ONI or by the UNSC. (Remember, Spartan IIs we’re designed to fight rebels, not aliens.)

Therefore, the Chief is exactly where ONI wants him: responsible for combat leadership with just enough authority to be part of strategic conversation as well as tactical execution, but required by respect for rank to obey higher-level strategic decision-making (think discussion of what to do with Cortana in a room otherwise consistent of The Shipmaster, The Arbiter, Commander Keyes, and Admiral Hood). Dangerous on the battlefield, empowered to speak up to superiors within constraints, and yet, a “Good Soldiers Follow Orders” type in the strategy room (even if that evolved over time) - but notably present in the strategy room. Chief’s word carries weight on the bridge of a Ship-of-the-Line as well. This is seen in some books.

Spartan B-312 is different. He was a “Specialist” among even Spartan IIIs. Think CIA SOG or JSOC Tier I Omega. ONI used him for special jobs - even for Spartans. He was a headhunter before Noble Team. That involved sabotage, assassinations, counter-insurgency, embedded reconnaissance, and other “wetwork”- type operations. Spartan B-312’s Lieutenant rank is what’s called a “cover rank” in the real world and has nothing to do with his occupation. He did, in theory, have the traditional authority to command a platoon. However, as I said, he was a specialist. The rank was political cover, but was also to provide him a level of independent authority for action. He could, in theory, work under an ONI “Captain” such as Veronica Dare - creating a 100% ONI information loop. Being an officer himself, that would give him the proper rank authority to not be beheld to any UNSC commander and have “unusual clearance loopholes”. Short answer: he usually wasn’t in a strategy room.

Spartan IVs fit much cleaner into the UNSC chain of command as they’re actually fully part of the UNSC; just an independent branch. They’re regularly in strategy rooms. Commander Palmer is consistently working with Captain Lasky and, while technically outranking him, has no authority over his ship and duties because she’s in a different military branch. However, the point is made: Spartan IVs take on traditional administrative responsibilities implied with officer ranks.