Yup you can play the whole game without Co-Op. It's great.
Immersive is perfect. Enemies don't have a level. It's you v them.
"Once the update lands, Breakpoint players will have three options to choose from; there's the Regular Experience, enabling those that actually like the game's original flavour to play on, while the radical stuff can be found in the Immersive Experience. This, says Ubisoft, "removes gear level and tiered loot entirely, and offers a bunch of new tactical options." It also features partial health regeneration, limited resources, a minimal interface, and normal difficulty.
Just doing a spot of the old "realistic looting".
There's also a third, highly configurable Custom Experience, enabling players to choose their favourite elements of both modes and adjust various community-requested settings. They can, for instance, select to disable weapon quality tiers and item levels, choose whether to carry one or two primary weapons, enable realistic looting and ammo loss on reload, adjust stamina levels and bandage quantity, set frequency of injury status, tweak health regeneration, and more.
There are also new HUD settings, and a new Private Mode limited to story characters and co-op teammates."
Bolded the good stuff. You can basically play it anyway you want now!