Octane's Underwhelming Passive Exists To Make Up For An Underwhelming Tactical
So Octane's passive is that he regenerates 1 health every 2 seconds while not taking damage.
Using Octane's stim takes away 10 health.
This means that in order for Octane's passive (which exists to make up for the health drain of speed) to make up for the cost of using stim Octane needs to not take damage for 20 seconds. This in a way means Octane's stim has a 20 second cooldown.
So in exchange for 10 health you get to use Bangalore's passive for 6 seconds while making a wubwubwubwubwub sound and leaving a bright neon trail. And it sort of has a 20 second cooldown.
Takeaway: Octane's passive does a poor job at making up for the use of each stim (which is in and of itself kind of underwhelming for the cost) and offers no real benefit in or out of fights. Remember! It takes FIFTY SECONDS to passively regenerate a syringe worth of health.