I'd still bet on a flawed load order, or missing mods, but there could be other reasons.
It would be relatively easy to implement a perk line (maybe 3 levels) to improve the duration and slow down of bullet time.
You could call it "Adrenaline Rush", from Fo2. The function doesn't quite fit the original ("Gain +1 Strength when you drop below 50% of your max HP."), but the name still fits the new function. Or you could just call it "Bullet Time" I guess.
Most of the alternative starts should get Rank 1, but some of them, (Politician, Mechanic) could make up for it in other ways.
Another more radical option would be to use "Fast Shot" from the older fallouts: "You don't have time to aim for a targeted attack, because you attack faster than normal people". It would replace VATS with Bullet Time. Perhaps it's too extreme for most people?..
Edit: By the way, does BT count as VATS for the purposes of damage taken (generally reduced in VATS) perks like "Grim Reaper's Sprint" (restores AP on a kill during VATS) etc? I'm guessing on No, but it would be interesting to know. Could be interesting to know for custom perks as well.