What?
Why are you comparing 1xChaos Bolt to 3xIncinerate? It's not like you'd cast 3 incinerates if you were looking to maximize overall damage with or without the glyph. You should be comparing 2 buffed Chaos Bolts to getting out more unbuffed Chaos Bolts more frequently. A extremely basic calculation would be something like the following:
With Glyph: 2 Chaos Bolts per Minute.
Without Glyph: 2.4 Chaos Bolts per Minute (2 Chaos Bolts per 50 seconds = 2.4 Chaos Bolts per Minute (2/50 * 60)
Thus in order for glyph to be worth it, you'd need to be getting more than .4 Chaos Bolts worth of damage out of your second Chaos Bolt. However, that assumes procs, and obviously you'll be getting procs for both Chaos Bolts in both cases (potentially), so overall it'd depend on your likelyhood to get procs on your second non-glyphed Chaos Bolt. It's somewhat close, but I'm not sure I'd call it better in all cases. I especially don't get your comparison to 3 incinerates.
Even with the glyph I doubt you'd be using it on CD if your aim was to get both buffed with trinkets, which only decreases it's worth compared to un-glyphed.
As for Sac, your observation is based on personal experience with people who may be playing at a skill level far beneath your own. Not exactly a valid comparison.
As for your comment on 3 ticks of damage, I don't think you properly understand DoT snapshotting nor how GoSac works. When your CB hits it does full damage, and applies a DoT that ticks 3 times for a percentage of the original hit. The DoT is snapshotted based on how much damage the original hit did. There's no damage loss to GoSac inherent in that nature, nor is it a big loss if you get the cast off during Black Blood. The only argument you could potentially make would be Skull Banner, since the crit damage is only boosted while you have the buff, but that's such a small and infrequent case, and the damage you'd lose is so small that it's really not even worth considering.