I liked how the armor customization aspect of Reach's multiplayer was more lengthy to progress through and offered variants of certain pieces (helmet attachments), but let's not try and give canon reasons for this.
Honestly, do you think that before a space mission an officer will say "Alright Spartans! Lock 'n load! Be ready in... Wait a minute. Where's your EVA gear, son?", with a Spartan replying that he can't afford/unlock the EVA variant yet (although humorous, I couldn't shake the unbelievable nature of this). Do you think it makes sense to force conscripted orphaned soldiers to PAY for the equipment they need? Do you think Spartans are paid Cr for a life after the war?
To clarify, I'm not against the system of unlocking/purchasing armor. I just don't want to see it given any context in story or logic, because it doesn't need it and it won't add anything positive.
As for perks linked to armor (EOD having 50% explosive resistance), I am wholeheartedly against that concept in its entirety. Halo is, or at least was, based around Equal Starts (everyone spawning with the same equipment/stats) and the Golden Triangle (guns, grenades, and melee). Having perks implemented like this, as a passive and non-changeable modifier during a life/match, derails both of these principles. What's more is that linking perks to armor will make players choose armor based on their effects, rather than their aesthetics.