Here's the thing. In every good halo title you had a strong starting weapon. There was never a need to pick up an alternative rifle. You use the starting weapon and pick up POWER weapons. I don't know why the magnum can't be ok. The starting weapon is supposed to be a jack of all trades. We don't need 6 rifles to pick up.
Overall you're incorrect; though, you're right on some accords.
Yes, the default loadout provided players the Pistol which made the majority of the sandbox outside of tier 1 (power) weapons irrelevant. The other loadout weapon was the AR which was more or less regulated to an emergency or clean-up option.
No, the default loadout gave players an SMG and Pistol. Both were dual wield-able weapons that were weak on their own and both had quite limited range. Initially the Pistol was semi-usable as a standalone weapon and quite deadly when paired with a second weapon, but Bungie released an early patch that reduced its lethality so that it wouldn't be over-powering in its dual use role, but also effectively killed any of its stand alone use. Nevertheless, most (minus the Needler unless you managed to shoot 3 Needlers) map pick-ups were very important toward improving your lethality. However, Bungie adopted the BR as the starting weapon for the Big Team playlists shortly after the game's release because they quickly realized the game-play suffered greatly on big maps with the default loadout. Also, the Team Hardcore playlist mimic'd MLG's settings which gave players the BR as the starting weapon; the BR certainly limited the need to pick-up anything less than Tier 1 power weapons.
No, the default loadout gave players arguably the weakest Pistol within the franchise (though it was dual wield-able) and returned the limited AR to the franchise. Again, both weapons could be out dueled by the majority of the sandbox and had fairly limited range, so map pick-ups were quite important toward improving your chances to earn kills. The BTB, Squad Battle, and Hardcore/MLG playlists did provide BR starts which again limited the need to pick-up anything less than Tier 1 weapons, but the vast majority of playlists provided players with the default Pistol & AR loadout. There was also periodic/temporary playlists that would appear such as Team BRs and Team Throwback which provided BR starts too.
No & Yes. Like H2 & H3 some playlist provided you with the prominent precision weapon as your starting weapon, but the majority didn't; plus, loadout options diversified the potential for players to have different loadout weapons within the same match.
Similar to H:CE in that the modified Reach Pistol that was meant to mimic the CE Pistol significantly reduced the need to pick up or use anything other than Tier 1 weapons.
Custom loadouts primarily dictated what players would start with. Some playlists didn't offer players choices or limited their options, but most playlists gave players the freedom to choose what they wished to start with.
The default loadouts varied depending on what players voted for within the match selection process. BR starts would limit the need to pick-up anything other than Tier 1 weapons. Side note: the H2A Pistol received stronger lethality than the patched classic H2 version. Also, this game includes an AR where as classic H2 didn't include it and if I recall correctly I think it was used as the starting loadout weapon for several game-type selections.
Provided a competent Pistol along with a competent AR as the primary starting weapons. The re-tuning changes have improved the standing of the Magnum within the sandbox to the point where players are less likely to pick-up non-tier 1 weapons over it. They should be looking to further tweak the BR, DMR, Carbine, SMG, and possibly the AR to better align them with the H5 standard Pistol.