But again if you do this by limiting things then you create a narrow sandbox or create a weird lots of one off pickups.
For the record I could vote for PV and boltshot need.
Would you consider past Halo games as having narrow sandboxes? I wouldn't. Vision/Camo/Jetpack would take the place of former powerup placements, and past Halo games had a ton of weapons on the map at the time, all of which had different uses and could potentially be controlled. I don't think there's any correlation between removing something in a loadout while placing it as a static element on maps and somehow narrowing the sandbox. You just have to execute properly on the idea, is all.
re: the power sandbox having more weapons - sure, and I'll be the first to say that I'd axe a few of them from matchmaking entirely (Incineration Cannon and Binary Rifle in particular) because I don't find them to be well-balanced, especially in combination with certain perks. It's just my opinion, and you're free to disagree with it, but a smaller sandbox of well-designed, well-implemented weapons will always be a more satisfying experience to me than a bloated sandbox full of things that don't necessarily fit with how the developer wants to use them. Stuff like the abilities and boltshot I think would be fine in a context of conflict arising around them at fixed points on the map. We'll see what the balance changes bring, but I'll take a system where elements like that can be affected and taken out of play by player action any day, which we don't see happening with the loadout system quite as much. It's just a design philosophy that resonates with me.